Add album lyrics endpoint with Spotify album pagination

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Motivation

• Provide a new API endpoint to fetch lyrics for an entire Spotify album by reusing the existing single-track lyric lookup logic.
• Support input as either album_url or album_id and handle Spotify API pagination for albums with many tracks.
• Return a sensible consolidated structure containing album metadata and per-track lyrics and synced lyrics.

Description

• Added backend/api/spotify/getAlbumTracks.mjs which extracts an album id, fetches album metadata, and pages through https://api.spotify.com/v1/albums/:id/tracks to collect all tracks.
• Extended backend/api/getLyrics.mjs with buildTrackLyrics (tries getLyricsBySignature, getLyricsByQuery, then getLyricsFromSpotify) and added getAlbumLyrics to aggregate per-track results and return { data: { albumName, imageUrl, tracks } }.
• Wired the new handler into routes by adding router.get('/getAlbumData', getAlbumLyrics) in backend/api/routes/routes.mjs and exported getAlbumLyrics.

Testing

• No automated tests were run for these changes.
• There are no CI or unit-test results to report for this PR.

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Codex Task