feat: add audio quality selector (standard to jymaster/Hi-Res)

- MusicProvider interface: setQuality/getQuality methods
- NeteaseProvider: passes quality level to /song/url/v1
- Default: exhigh (320kbps MP3)
- Settings page: 6-option grid selector
- GET/POST /api/music/quality endpoints

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

src/music/provider.ts

@@ -57,7 +57,9 @@ export interface MusicProvider {
   readonly platform: "netease" | "qq";
 
   search(query: string, limit?: number): Promise<SearchResult>;
-  getSongUrl(songId: string): Promise<string | null>;
+  getSongUrl(songId: string, quality?: string): Promise<string | null>;
+  setQuality(quality: string): void;
+  getQuality(): string;
   getSongDetail(songId: string): Promise<Song | null>;
   getPlaylistSongs(playlistId: string): Promise<Song[]>;
   getRecommendPlaylists(): Promise<Playlist[]>;