feat(navidrome): Musikserver-Integration (Subsonic API)

- NavidromeService mit Credential-Verwaltung (secure storage)
- Navidrome-Settings in Settings-Tab: Login/Logout für Server-Verbindung
- Dependencies hinzugefügt: http, crypto, shared_preferences, flutter_secure_storage
- Tests: 70/70 grün
- Analyzer: ✅ keine Fehler

Co-Authored-By: Claude Haiku 4.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01XJzQjUtnvYUtHdnTs3iCru

macos/Flutter/GeneratedPluginRegistrant.swift

@@ -9,7 +9,9 @@ import audio_service
 import audio_session
 import device_info_plus
 import file_picker_darwin
+import flutter_secure_storage_darwin
 import just_audio
+import shared_preferences_foundation
 import sqflite_darwin
 
 func RegisterGeneratedPlugins(registry: FlutterPluginRegistry) {
@@ -17,6 +19,8 @@ func RegisterGeneratedPlugins(registry: FlutterPluginRegistry) {
   AudioSessionPlugin.register(with: registry.registrar(forPlugin: "AudioSessionPlugin"))
   DeviceInfoPlusMacosPlugin.register(with: registry.registrar(forPlugin: "DeviceInfoPlusMacosPlugin"))
   FilePickerPlugin.register(with: registry.registrar(forPlugin: "FilePickerPlugin"))
+  FlutterSecureStorageDarwinPlugin.register(with: registry.registrar(forPlugin: "FlutterSecureStorageDarwinPlugin"))
   JustAudioPlugin.register(with: registry.registrar(forPlugin: "JustAudioPlugin"))
+  SharedPreferencesPlugin.register(with: registry.registrar(forPlugin: "SharedPreferencesPlugin"))
   SqflitePlugin.register(with: registry.registrar(forPlugin: "SqflitePlugin"))
 }