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)

android/app/src/main/AndroidManifest.xml

@@ -3,6 +3,7 @@
     <uses-permission android:name="android.permission.INTERNET"/>
     <uses-permission android:name="android.permission.FOREGROUND_SERVICE"/>
     <uses-permission android:name="android.permission.FOREGROUND_SERVICE_MEDIA_PLAYBACK"/>
+    <uses-permission android:name="android.permission.FOREGROUND_SERVICE_SYSTEM_EXEMPTED"/>
     <uses-permission android:name="android.permission.WAKE_LOCK"/>
     <uses-permission android:name="android.permission.RECORD_AUDIO"/>
     <uses-permission android:name="android.permission.SCHEDULE_EXACT_ALARM"/>
@@ -53,7 +54,7 @@
 
         <service
             android:name=".PluriWaveAlarmService"
-            android:foregroundServiceType="mediaPlayback"
+            android:foregroundServiceType="mediaPlayback|systemExempted"
             android:exported="false" />
 
         <!-- Receptor de controles de media (auriculares, notificación) -->