fix: collapse hero gap after analyze, prefer tracks with album art

fix: remove duplicate closing brace syntax error

feat: randomize search terms and offset for varied track results

feat: use Musixmatch lyrics search for source song detection (Spotify-style)

fix: detect source song by matching title words in input, not input in title

fix: use 5-word sequential phrase matching for lyrics source detection

feat: pin source song first when input looks like lyrics

fix: score tracks by search-rank position when audio features unavailable

cleanup: remove debug fields from recommend response

debug: add _debug counts to recommend response

fix: replace deprecated /recommendations with /search (Spotify Nov 2024 policy)

refactor: move backend files into backend/ directory