Feature: Advanced App Backup (v2), Native Spatializer (API 32+) & UI Polish

[YisusPineapple]

Description

This pull request significantly modernizes Lune's infrastructure by introducing a full-featured Application State Backup & Restore Engine (Backup v2) and migrating to the platform-native Spatializer API (API 32+) to resolve legacy deprecation warnings under Android 15 (targetSdk 36). It also includes UI refinements and localized Spanish corrections.

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Key Enhancements

1. Advanced Application State Backup & Restore (v2)

• Favorites & Metadata Overrides: The backup engine now serializes and restores the entire song_overrides database table [MusicDatabase.kt]. This preserves customized metadata (titles, artists, genres), custom local covers, and all liked/favorite statuses (isFavorite = true).
• Lune Settings: Serializes the complete state of SettingsManager using a type-safe nested data model (SettingsBackupData). This prevents type-safety issues during GSON deserialization and guarantees exact recovery of audio configurations, layout preferences, and custom themes.
• Accumulated Statistics: Packages the SQLite playback_stats table to preserve home screen cards and overall stats across device migrations.
• Backward Compatibility: Fully guaranteed. If a legacy v1 backup (containing only playlists) is imported, the engine falls back gracefully to playlist-only restoration without throwing exceptions.

2. Material 3 Expressive Loader & Thread Safety

• Replaced instantaneous toasts with a Material 3 non-dismissible AlertDialog during file I/O operations.
• The loader employs the hardware-accelerated CircularWavyProgressIndicator driven by a lightweight, infinite-loop transition—providing smooth expressive rendering friendly on modest devices.
• Implemented a step-by-step state transition ("Importing..." ➔ "Finalizing restoration...") backed by a 1200ms coroutine delay. This ensures that SQLite transactional writes and journal files are fully flushed on disk before recreating the active Activity context.

3. Native Spatial Audio Engine (API 32+)

• Dynamic Spatializer Configuration: Configures platform-native spatialization behavior on modern Android 12+ (API 32+) devices by programmatically setting setSpatializationBehavior(AudioAttributes.SPATIALIZATION_BEHAVIOR_AUTO) during MediaPlayer instantiation (playSong and performCrossfade). If disabled, it falls back cleanly to SPATIALIZATION_BEHAVIOR_NEVER.
• Stable Fallback Pipeline: Devices running on older platform versions below API 32 continue utilizing Lune's high-fidelity Virtualizer audio effect bound to the active MediaPlayer audio session ID, maintaining stable backward compatibility and eliminating compiler deprecation warnings under API 35/36.

4. Dynamic Language & UI Hot-Reload

• On successful import, the engine dynamically invokes AppCompatDelegate.setApplicationLocales(LocaleListCompat.forLanguageTags(code)) on the Main Thread and triggers an immediate context recreate() to apply the restored language and theme configurations without requiring a manual app restart.

5. Spanish Localization Cleanup

• Fixed inconsistent English strings in Spanish resources (values-es/strings.xml):
  • "Cover player" ➔ "Carátula del reproductor"
  • "Control player" ➔ "Controles del reproductor"
  • "Export/Import Playlists" ➔ "Exportar/Importar copia de seguridad"
• Fully localized standard options (Shuffle, Timer, Lyrics, Automix, etc.) for a polished native user experience.

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Technical Specifications

• Minimum SDK: 24 (Tested and verified on Android 15 / targetSdk 36).
• Concurrency: Heavy I/O disk writes and Room database transactions are strictly bound to Coroutines running on Dispatchers.IO to keep Dispatchers.Main lightweight and prevent frame drops.
• R8 Minification Safety: All new backup-specific data structures are protected from obfuscation under Lune's general ProGuard rules.