feat(eq): restyle equalizer screen and add custom presets

Restyle the Ecualizador settings screen to the new visual language while
keeping the equalizer at 5 bands (spike-resolved, Engram id 2498 - band
count is device-reported via just_audio's AndroidEqualizer, not app-chosen;
the approved mockup's 7 sliders would silently no-op on typical hardware).

- Restyle EcualizadorWidget in place: strip its internal title + preset
  chip row (the pushed screen's header now carries the title), add a
  habilitado parameter that greys/disables every slider when EQ is off.
  Widen PresetsEcualizadorWidget additively (personalizados param) so
  custom presets can join the chip row without a second implementation.
- Add servicio_presets_personalizados.dart (new file, own SharedPreferences
  key eq_custom_presets_v1) for custom EQ preset persistence - kept out of
  servicio_ecualizador.dart, which has an empty-git-diff success criterion
  for this change. preset_ecualizador.dart is unchanged: a custom preset is
  just a PresetEcualizador with a user-supplied name.
- Extend EstadoEcualizador with presetsPersonalizados,
  guardarPresetPersonalizado (validates non-empty name),
  eliminarPresetPersonalizado. The load is a new explicit
  cargarPresetsPersonalizados(), deliberately NOT folded into
  cargarPersistido(): that method is exercised ~30 times by
  estado_ecualizador_test.dart (protected, must stay unmodified) via Fakes
  only, with no SharedPreferences awareness in that file.
- Build out the Ecualizador screen body: base-vs-per-station explainer
  banner, a "Salida activa" row surfaced on the main screen (previously
  Advanced-only), an "Emisoras con ajuste propio" drill-down sourced from
  the existing presetsPorEmisora map, and a "Guardar como preset" action.

New coverage lives in new files rather than touching the three protected
EQ test files: ecualizador_widget_test.dart (component-level, did not
exist before this commit), servicio_presets_personalizados_test.dart, and
estado_ecualizador_presets_personalizados_test.dart. servicio_ecualizador.dart,
servicio_audio.dart and the three protected EQ test files keep an empty
git diff. Full suite: 713/713 green (2 skipped, unchanged), up from 682.

size:exception - realized 1,954 changed lines (25 files, plus this docs
update) against the 400-550 forecast: lib/ + ARB alone is ~650 lines, near
the top of the forecast band by itself since this WU also had to build out
a screen body WU3a only stubbed; the rest is 4 test files (675 lines) and
11 new ARB keys regenerating 13 lib/l10n/gen files (~546 lines) - the same
pattern every prior work unit in this branch has hit. Not splittable: WU14
reuses this unit's editor component by exact runtime type and cannot begin
until this lands as a whole.

openspec/changes/rediseno-funcional/tasks.md

@@ -51,7 +51,7 @@
 | 9 | `feat(vacaciones): add vacation range manager screen` | 8 | 350-450 | Medium | Monitor |
 | 10 | `feat(alarmas): rewrite alarm editor with inline time widget` | 8 | 500-650 | High | **Yes — indivisible new widget**‡ |
 | 11 | `feat(alarma-sonando): restyle ringing screen, drop live countdown label` | 1 | 200-300 | Low (safety-critical review attention: High) | No |
-| 13 | `feat(eq): restyle equalizer screen and add custom presets` | 3a | 400-550 | Medium-High | Monitor |
+| 13 | `feat(eq): restyle equalizer screen and add custom presets` | 3a | ~~400-550~~ → **REALIZED: 1,871** (1,793+ / 78-, 25 files) | Medium-High | **Yes — retroactive, see WU13 section** |
 | 14 | `feat(reproductor): restructure full player with tool-tray and EQ sheet` | 13 | 450-600 | Medium-High | Monitor |
 | 15 | `feat(grabaciones): add recordings library screen` | 3b | ~~300-400~~ → **REALIZED: 1,767** (1,767+ / 0-, 22 files) | Medium | Monitor§ |
 | 15b | `fix(grabaciones): wire the recordings library into Settings navigation` | 15 | 60-100 | Low | No |
@@ -735,32 +735,67 @@ Stations-With-Own-EQ Drill-Down, Base-vs-Per-Station Explainer Preserved, Active
 > **Hazard, restated: persistence for custom presets must NOT go in `servicio_ecualizador.dart`.** That file has an
 > empty-`git diff` success criterion.
 
-- [ ] 13.1 RED — the Ecualizador screen renders exactly **5** vertical sliders (regression guard — reject any
-       future 7-slider change on sight).
-- [ ] 13.2 RED — `servicio_presets_personalizados_test.dart`: save/list/delete round-trip for a named custom preset
+- [x] 13.1 RED — the Ecualizador screen renders exactly **5** vertical sliders (regression guard — reject any
+       future 7-slider change on sight). **Corrected at apply time**: named test file `ecualizador_widget_test.dart`
+       did not exist before this commit (`ecualizador_widget.dart` had zero coverage) — created new, plus the
+       screen-level assertion in `pantalla_ajustes_ecualizador_test.dart` (the spec scenario's own GIVEN is "the
+       Ecualizador settings screen").
+- [x] 13.2 RED — `servicio_presets_personalizados_test.dart`: save/list/delete round-trip for a named custom preset
        via its **own** SharedPreferences key `eq_custom_presets_v1`.
-- [ ] 13.3 RED — submitting an empty/whitespace-only preset name shows a validation message and persists nothing.
-- [ ] 13.4 RED — the "Emisoras con ajuste propio" drill-down lists exactly the stations present in
+- [x] 13.3 RED — submitting an empty/whitespace-only preset name shows a validation message and persists nothing.
+       Covered at both the state layer (new `estado_ecualizador_presets_personalizados_test.dart` — see 13.7's note)
+       and the UI layer (`pantalla_ajustes_ecualizador_test.dart`'s "Guardar como preset" dialog scenarios).
+- [x] 13.4 RED — the "Emisoras con ajuste propio" drill-down lists exactly the stations present in
        `presetsPorEmisora`.
-- [ ] 13.5 RED — the "Salida activa" row is visible on the main screen (not only Advanced) and updates on a
+- [x] 13.5 RED — the "Salida activa" row is visible on the main screen (not only Advanced) and updates on a
        simulated device change; the base-vs-per-station explainer banner is visible.
-- [ ] 13.6 GREEN — create `lib/servicios/servicio_presets_personalizados.dart` (**new file**, own SharedPreferences
+- [x] 13.6 GREEN — create `lib/servicios/servicio_presets_personalizados.dart` (**new file**, own SharedPreferences
        key). **Do NOT add any member to `servicio_ecualizador.dart`.** `lib/modelos/preset_ecualizador.dart` stays
        unchanged — a user preset is a `PresetEcualizador` with a user-supplied `nombre`; `toJson`/`desdeJson`
        already exist.
-- [ ] 13.7 GREEN — extend `EstadoEcualizador` with `presetsPersonalizados`, `guardarPresetPersonalizado(nombre)`,
-       `eliminarPresetPersonalizado(nombre)`, reading/writing only through the new service.
-- [ ] 13.8 GREEN — restyle `lib/widgets/ecualizador_widget.dart` in place: strip the internal title + preset chip
-       row (lines 59-77 — the pushed header now carries the title), restyle the 5 `Card`/`RotatedBox`/`Slider`
-       tiles to the vertical-track look, add the `habilitado` parameter. Keep the `for (int i = 0; i < 5; i++)`
+- [x] 13.7 GREEN — extend `EstadoEcualizador` with `presetsPersonalizados`, `guardarPresetPersonalizado(nombre)`,
+       `eliminarPresetPersonalizado(nombre)`, reading/writing only through the new service. **Correction found at
+       apply time**: the new custom-preset LOAD (`cargarPresetsPersonalizados()`) is deliberately NOT folded into
+       `cargarPersistido()` — that method is exercised ~30 times by `estado_ecualizador_test.dart` (one of the three
+       protected EQ test files) via Fakes for `servicio`/`dispositivoAudio` ONLY, with zero SharedPreferences
+       awareness anywhere in that file; adding a third always-real-by-default collaborator to it would have
+       introduced real SharedPreferences I/O into every one of those cases. Called explicitly from the screen's
+       `initState` instead (same pattern `refrescarDispositivoActual` already uses). New coverage lives in a NEW
+       file, `test/estado/estado_ecualizador_presets_personalizados_test.dart` — NOT added to
+       `estado_ecualizador_test.dart`, which stays unmodified.
+- [x] 13.8 GREEN — restyle `lib/widgets/ecualizador_widget.dart` in place: strip the internal title + preset chip
+       row (re-verified at the CURRENT lines 59-77 of the pre-WU13 file, not trusted from the design doc's
+       reference), restyle the 5 `Card`/`RotatedBox`/`Slider` tiles to the vertical-track look (token-driven accent
+       colour, `AnimatedOpacity` grey-out), add the `habilitado` parameter (disables + greys every slider).
+       `PresetsEcualizadorWidget` additively widened with an optional `personalizados` list (default empty) so
+       custom presets can join the chip row without a second implementation. Kept the `for (int i = 0; i < 5; i++)`
        loop bound literally `5`.
-- [ ] 13.9 GREEN — build `lib/pantallas/ajustes/pantalla_ajustes_ecualizador.dart` wiring
-       `EstadoEcualizador.presetPrincipal` / `cambiarPresetPrincipal`, surfacing "Salida activa" and the drill-down
-       row.
-- [ ] 13.10 REFACTOR — reviewer check: confirm `git diff` is **empty** for `lib/servicios/servicio_ecualizador.dart`,
+- [x] 13.9 GREEN — build out `lib/pantallas/ajustes/pantalla_ajustes_ecualizador.dart` (the WU3a placeholder body)
+       wiring `EstadoEcualizador.presetPrincipal` / `cambiarPresetPrincipal`, surfacing "Salida activa" (own private
+       row, live via the existing device-change `notifyListeners()`) and the drill-down row (own private row +
+       destination screen, station uuids resolved against `EstadoRadio.listaFavoritos` with a raw-uuid fallback for
+       a non-favorite station). Added the base-vs-per-station explainer banner and the "Guardar como preset" action
+       + dialog (validates via `guardarPresetPersonalizado`, shows an inline `errorText` on empty/whitespace name).
+- [x] 13.10 REFACTOR — reviewer check: confirmed `git diff` is **empty** for `lib/servicios/servicio_ecualizador.dart`,
        `lib/modelos/preset_ecualizador.dart`, and the band-application block at
-       `lib/servicios/servicio_audio.dart:749-762`.
-- [ ] 13.11 Verify — the three EQ test files pass **unmodified**; exactly 5 sliders render.
+       `lib/servicios/servicio_audio.dart:749-762` (this WU never touches `servicio_audio.dart` at all).
+- [x] 13.11 Verify — the three EQ test files (`servicio_ecualizador_test.dart`, `estado_ecualizador_test.dart`,
+       `servicio_audio_eq_reapply_test.dart`) pass **unmodified**; exactly 5 sliders render (component AND screen
+       level). Full suite: 713/713 green (2 skipped, unchanged), up from 682. `flutter analyze`: 1 issue, identical
+       to baseline. Literal-encoding scan: zero hits.
+
+**`size:exception` recorded.** Realized: **1,871 changed lines** (1,793+/78-) across 25 files against the 400-550
+forecast — same "a strict-TDD commit carries its test files, and any ARB touch drags 13 generated files with it"
+pattern as every prior WU (Engram `reference/estimating-strict-tdd-diffs`, id 2514). Breakdown: `lib/` production
+code alone is 628 lines (`pantalla_ajustes_ecualizador.dart` +326, `ecualizador_widget.dart` restyle ~151,
+`estado_ecualizador.dart` +64, new `servicio_presets_personalizados.dart` +87) plus 22 ARB source lines — at the top
+edge of the forecast band by itself given this WU also had to build out a screen body WU3a only stubbed; the 4
+test files (2 new state/service-layer files plus the widget test and the extended screen test) add 675 lines, and
+11 new ARB keys drag in 546 more via the 13 regenerated `lib/l10n/gen/*.dart` files. Justification: the restyle,
+the new persistence service, the state-layer extension and the screen wiring (explainer/salida-activa/drill-down/
+save-flow) are one cohesive vertical slice — WU13 must land as a whole before WU14 can reuse its editor component
+by exact runtime type; splitting further would leave either an unstyled widget with no screen consumer or a screen
+half-wired to a service that doesn't exist yet.
 
 ## WU14 — Reproductor completo + per-station EQ sheet