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/l10n/gen/app_localizations_it.dart

@@ -439,6 +439,9 @@ class AppLocalizationsIt extends AppLocalizations {
   String get recordingDeleteConfirmMessage =>
       'Esta acción no se puede deshacer.';
 
+  @override
+  String get recordingsLibrarySettingsTooltip => 'Ajustes de grabación';
+
   @override
   String get stationOrderTitle => 'Ordine emittenti';