feat(alarms): native reliability fixes and end-to-end snooze

- Use mediaPlayback|systemExempted FGS type with FOREGROUND_SERVICE_SYSTEM_EXEMPTED so alarms fire on Android 14+ (FOREGROUND_SERVICE_ALARM does not exist in the SDK)
- Deduplicate fire notifications: the foreground service FSI notification is the single owner; receiver path removed
- Notification channel v2 with alarm sound URI and USAGE_ALARM attributes, one-time guarded migration from legacy channels
- Pass fallback station through the MethodChannel (NativeAlarmSpec schemaVersion 3) with a three-stage audio chain: primary -> fallback station -> bundled WAV
- Native fade-in volume ramp honoring fadeInSegundos when the app is killed
- Request battery-optimization exemption once, tracked with a persisted asked-once flag
- Fix snooze end-to-end: native ACTION_SNOOZE now reports back to Flutter (snoozed event + cold-start sync), snooze anchor unified to occurrence+minutes on both sides, periodic recalc no longer erases an active snooze
- Add snooze buttons (3/5/10/custom) to the ringing screen with shared audio teardown
- Redesign ringing screen on PluriWaveScaffold with reduced-motion-aware entry animation (new PluriAnimate helper)
- Alarm editor: live next-trigger preview, searchable station pickers (primary and fallback), configurable snooze duration, volume floor down to 0
- New alarm strings localized across all 13 locales
- New unit/widget tests for the snooze flow, alarm bridge payloads, ringing screen and editor (77 tests green)
- SDD artifacts for the app-quality-and-native-alarms change (explore, proposal, spec, design, tasks, apply progress)

lib/l10n/gen/app_localizations.dart

@@ -1510,6 +1510,36 @@ abstract class AppLocalizations {
   /// **'Sin emisora: usar sonido interno'**
   String get noStationUseInternalSound;
 
+  /// No description provided for @alarmFallbackStationLabel.
+  ///
+  /// In es, this message translates to:
+  /// **'Emisora de respaldo'**
+  String get alarmFallbackStationLabel;
+
+  /// No description provided for @alarmStationPickerSearchHint.
+  ///
+  /// In es, this message translates to:
+  /// **'Buscá una emisora por nombre'**
+  String get alarmStationPickerSearchHint;
+
+  /// No description provided for @alarmSnoozeDurationTitle.
+  ///
+  /// In es, this message translates to:
+  /// **'Duración de la posposición'**
+  String get alarmSnoozeDurationTitle;
+
+  /// No description provided for @snoozeAction.
+  ///
+  /// In es, this message translates to:
+  /// **'Posponer'**
+  String get snoozeAction;
+
+  /// No description provided for @alarmSnoozeOptionLabel.
+  ///
+  /// In es, this message translates to:
+  /// **'{minutes} min'**
+  String alarmSnoozeOptionLabel(int minutes);
+
   /// No description provided for @saveFavoritesAlarmHint.
   ///
   /// In es, this message translates to: