fix(chrome): retire PluriScreenHeader, it has no equivalent in the prototype

PluriScreenHeader was a 38-radius glass hero: an aurora banner at 24%
opacity, a black-to-transparent scrim, two radial orbs, a 120px app-mark
watermark and a 56px tri-gradient glyph badge. None of it is in the
prototype (t4) -- every root's title is plain text in its own 56px
row, which PluriRootHeader (S1) already provides. Delete the class
(and its now-orphaned _Orb helper) and its four call sites (Buscar,
Favoritos x2, Alarmas, Ajustes landed with S8).

Two of those call sites carried the hero's only functional bit besides
the title, so PluriRootHeader gains an `actions` slot (rendered before
the shared bedtime button) to keep them reachable:
  - Alarmas' create-alarm button (FilledButton.tonalIcon, unchanged
    shape, just relocated)
  - Buscar's filters entry point (the same tappable PluriStatusPill,
    just relocated)
Every other retired trailing pill (Ajustes' "Secure" status,
Favoritos' collection-count badges, Alarmas' alarm-count badge) was
purely decorative and matches the prototype by simply disappearing.

S2, Tier 1 visual-fidelity pass (audit id 2521).

test/pantallas/root_header_wiring_test.dart

@@ -6,6 +6,7 @@ import 'package:pluriwave/estado/estado_alarmas.dart';
 import 'package:pluriwave/estado/estado_busqueda.dart';
 import 'package:pluriwave/estado/estado_ecualizador.dart';
 import 'package:pluriwave/estado/estado_grabacion.dart';
+import 'package:pluriwave/estado/estado_idioma.dart';
 import 'package:pluriwave/estado/estado_radio.dart';
 import 'package:pluriwave/l10n/gen/app_localizations.dart';
 import 'package:pluriwave/pantallas/pantalla_ajustes.dart';
@@ -24,11 +25,9 @@ import '../helpers/fakes_alarmas.dart';
 /// S1 (Tier 1 visual fidelity): `app.dart`'s `PluriWaveScaffold(appBar:
 /// AppBar(...))` is gone — every root now draws its own [PluriRootHeader]
 /// instead, matching the prototype (no screen in `t4` shows a global
-/// `AppBar`). Each root still ALSO carries its pre-existing
-/// `PluriScreenHeader` hero (S2 in this same Tier 1 batch replaces that
-/// separately), so title assertions below are scoped to [PluriRootHeader]'s
-/// own subtree — the title string itself still appears twice on screen
-/// until S2 lands.
+/// `AppBar`). [PluriRootHeader]'s own title text is asserted via
+/// `find.descendant` throughout — see `pluri_screen_header_retired_test.dart`
+/// for S2's separate assertion that the old glass-hero subtitle is gone.
 ///
 /// Pre-existing project constraint (see `pantalla_ajustes_test.dart`):
 /// PluriGlassSurface paints a background over ListTile's ink layer, which
@@ -72,6 +71,7 @@ void main() {
         ListenableProvider<EstadoEcualizador>.value(value: estado.ecualizador),
         ListenableProvider<EstadoGrabacion>.value(value: estado.grabacion),
         ListenableProvider<EstadoBusqueda>.value(value: estado.busqueda),
+        ChangeNotifierProvider<EstadoIdioma>.value(value: EstadoIdioma()),
         if (alarmas != null)
           ChangeNotifierProvider<EstadoAlarmas>.value(value: alarmas),
       ],