feat(albums): compilation filter toggle in All Albums

Tri-state button (all / only compilations / hide compilations) in the
Albums page header, using the OpenSubsonic isCompilation tag from
Navidrome. Client-side filter via useMemo, no extra server calls.
Closes #65.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/api/subsonic.ts

@@ -71,6 +71,8 @@ export interface SubsonicAlbum {
   created?: string;
   /** Present on some servers (e.g. OpenSubsonic) for album-level rating. */
   userRating?: number;
+  /** OpenSubsonic: true when the album is tagged as a compilation. */
+  isCompilation?: boolean;
 }
 
 /** OpenSubsonic `artists` / `albumArtists` entries on a child song (may include `userRating`). */