album_sort: add beets sidecar and switch repo to SSH

Created by: jedmund

Summary

• Add a beets sidecar to the album-sort stack, built from deploy/beets/ in the album-sort source repo, sharing the music volume and exposing web (8337) + API (8338) on the shared network
• Wire album-sort to beets via BEETS_WEB_URL / BEETS_API_URL env vars and depends_on: beets; create a new beets-data/ directory under the stack path
• Switch album_sort_repo from HTTPS to SSH (ssh://git@git.atelier.house:2222/...) and update the git task with accept_hostkey: true + become: false so the role can pull from Forgejo without a PAT

Test plan

• ansible-playbook deploy/album_sort.yml --check --diff shows expected compose changes
• Deploy for real; confirm album_sort_beets container builds and starts
• docker exec album-sort curl -s http://beets:8337 reaches the beets web UI
• album-sort picks up BEETS_WEB_URL / BEETS_API_URL and behaves as expected
• Source pull from Forgejo succeeds over SSH on first run (host key accepted)