Docs: install on Unraid (LinuxServer.io image) and the release smoke test

[KodeStar]

Hold until the image is live: merge only after linuxserver/docker-audiosilo#1 is merged, lscr.io/linuxserver/audiosilo has built, and the app shows up in Unraid's Community Applications. The developer pages also describe the smoke test from KodeStar/audiosilo-server#111, so merge that first.

• New user page Getting started > Install on Unraid: install from CA, the template fields (Appdata and PUID/PGID are under Show more settings), first-run credentials, HTTPS and reverse proxies via Server > Settings, updates, and moving from ghcr.io/kodestar/audiosilo-server (/data to /config, /library to /audiobooks, env vars, tls.cache_dir).
• Links to it from the Docker quick start, the docs home, and the manager's Unraid tip.
• Developer docs: release-pipeline gains the smoke test and the LinuxServer.io downstream; releasing gets "publish only once the run is green", the lsio row and the -rc pre-release caveat; documentation.md maps the page.

npm run build passes.