fix(grabaciones): wire the recordings library into Settings navigation

WU15 shipped PantallaGrabaciones (the recordings library: storage bar,
recording rows, the "..." Rename/Share/Delete menu) fully tested but
reachable from nowhere in the app - a gap flagged in WU15's own
apply-progress notes, not fixed there since it needed a design
decision rather than a guess.

Coordinator ruling applied: the approved mockup's "Ajustes > Grabaciones"
screen depicts the library, not the folder/size settings form. So the
GRABACIONES Y MUSICA group's "Grabaciones" row in pantalla_ajustes.dart
now opens PantallaGrabaciones instead of PantallaAjustesGrabaciones.
The settings form is not dropped - it stays reachable, now from within
the library via a settings icon in its PluriPushScaffold actions,
matching the existing pantalla_ajustes_timer_sueno.dart "Add" action
precedent for a real capability living in the header.

One new ARB key (en/es only, per precedent): recordingsLibrarySettingsTooltip.

Tests: 604 -> 605 (one scenario re-targeted in pantalla_ajustes_test.dart,
one new scenario in pantalla_grabaciones_test.dart, which needed the
same ListTile-ink-assertion suppression helper WU3a/WU3b established
since it now pushes a ListTile-bearing settings screen). flutter
analyze unchanged at 1 pre-existing info.

Recorded in tasks.md as WU15b - not part of the original 18-unit plan,
added here to close the gap WU15 flagged.

lib/pantallas/pantalla_grabaciones.dart

@@ -13,6 +13,7 @@ import '../widgets/pluri_icon.dart';
 import '../widgets/pluri_layout.dart';
 import '../widgets/pluri_premium_widgets.dart';
 import '../widgets/pluri_push_scaffold.dart';
+import 'ajustes/pantalla_ajustes_grabaciones.dart';
 
 /// Inline-preview playback + duration lookup for a single recording file at
 /// a time (WU15, recordings-library spec — "Row playback starts and
@@ -228,6 +229,17 @@ class _PantallaGrabacionesState extends State<PantallaGrabaciones> {
 
     return PluriPushScaffold(
       title: l10n.recordingsLibraryTitle,
+      actions: [
+        IconButton(
+          icon: const Icon(Icons.settings_outlined),
+          tooltip: l10n.recordingsLibrarySettingsTooltip,
+          onPressed:
+              () => PluriPushScaffold.push(
+                context,
+                (_) => const PantallaAjustesGrabaciones(),
+              ),
+        ),
+      ],
       body: FutureBuilder<List<ArchivoGrabacion>>(
         future: _grabaciones,
         builder: (context, snap) {