Merge PR #121: show requester names in play history

Merges feature/play-history-requester (@Fa1nttt) into main.

The PR records the WebUI/TeamSpeak requester on queued songs and persists it
to play history (schema migration for requestedBy), rendering it as a badge in
SongCard (gray for 游客/guest).

Conflicts (frontend platform union) resolved to keep both 'spotify' (from #118)
and the new requestedBy/playedAt fields.

Integration fix: the Spotify playback branch in resolveAndPlay (added by #118,
which did not exist on the PR's base) also records play history — added
`requestedBy: song.requestedBy` there so Spotify tracks carry attribution too,
matching the non-Spotify path.

Verified on the merged tree: tsc --noEmit clean, full suite 1309/1309, web build clean.

Co-Authored-By: Fa1nttt <noreply@github.com>
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

web/src/stores/player.ts

@@ -11,6 +11,8 @@ export interface Song {
   duration: number;
   coverUrl: string;
   platform: 'netease' | 'qq' | 'bilibili' | 'youtube' | 'local' | 'kugou' | 'spotify';
+  requestedBy?: string;
+  playedAt?: string;
 }
 
 export type Source = 'netease' | 'qq' | 'kugou' | 'spotify';