feat: youtube stats endpoint + nav link

feat(backend): POST /jobs/youtube + GET /jobs/youtube/{id}

Add pitch/tempo shifting on download

Set baseline stats to 100 visits and 5 downloads

Add admin dashboard with download history and persistent storage

Fix before-clip playback by persisting original in output dir

Add before/after clip preview and SEO landing pages

feat(stems): add multi-stem downloads with Playwright e2e coverage

feat(trim): add upload trim range with preview and backend segment processing

fix(backend): use asyncio.to_thread for stats IO, guard malformed JSON, isolate test side-effects

feat(backend): add file-based stats counter with /stats and /stats/visit endpoints

chore: pre-deployment cleanup and fixes

fix: threadpool executor for cleanup, shutdown hook, stronger download tests

feat: GET /download/{job_id} endpoint and APScheduler file cleanup

feat: demucs processing worker with asyncio queue and MPS acceleration

fix: cleanup on enqueue failure, MP3 magic byte validation, stronger upload tests

feat: POST /upload endpoint with MP3 validation and size limit

fix: init asyncio queue inside startup event, add QueueFull guard

feat: job store and GET /status/{job_id} endpoint

fix: anchor paths to __file__, add Field validation, trigger lifespan in tests

feat: backend scaffold with health endpoint and pytest setup