feat: add multilanguage support (i18n) for English and Indonesian

- Add flutter_localizations and intl dependencies
- Create l10n.yaml configuration and ARB files (app_en.arb, app_id.arb)
- Add L10n extension for easy context.l10n access
- Localize all active screens:
  - setup_screen, track_metadata_screen, log_screen
  - download_settings_page, options_settings_page, appearance_settings_page
  - extensions_page, extension_detail_page, extension_details_screen
  - about_page, provider_priority_page, metadata_provider_priority_page
  - home_tab, queue_tab, store_tab, main_shell
  - album_screen, artist_screen, playlist_screen
  - downloaded_album_screen, queue_screen
- Localize widgets: update_dialog, download_service_picker
- Technical terms (FLAC, API, Spotify, Tidal, Qobuz, etc.) are NOT translated
- ~900+ localized strings in English, ~660+ in Indonesian

pubspec.lock

@@ -382,6 +382,11 @@ packages:
       url: "https://pub.dev"
     source: hosted
     version: "1.0.3"
+  flutter_localizations:
+    dependency: "direct main"
+    description: flutter
+    source: sdk
+    version: "0.0.0"
   flutter_plugin_android_lifecycle:
     dependency: transitive
     description:
@@ -488,6 +493,14 @@ packages:
       url: "https://pub.dev"
     source: hosted
     version: "4.7.2"
+  intl:
+    dependency: "direct main"
+    description:
+      name: intl
+      sha256: "3df61194eb431efc39c4ceba583b95633a403f46c9fd341e550ce0bfa50e9aa5"
+      url: "https://pub.dev"
+    source: hosted
+    version: "0.20.2"
   io:
     dependency: transitive
     description: