docs(release): first public Linux release notes (#454)

[TheZupZup]

Closes #454.

One new file, docs/release-notes/linux-first-public-release.md. Based on main, touches nothing else, so it does not collide with the other Flatpak PRs.

The rule I wrote it to: a feature is listed as working only if it has been run on Linux, in the packaged Flatpak, with something checking it on every build. Passing unit tests do not qualify, and neither does "the Android app does this". That rule is what makes the limitations section the substantive half of the page.

What it claims

Only two things, both backed by smokes that now run on every build inside an actually-installed Flatpak: local library (scan, tags from the files' own metadata, embedded artwork, skipped files counted) and playback on the packaged libmpv (transport asserted on the playback clock, not on a status flag).

Plus the sandbox behaviour, which is checked the same way.

What it says is not validated

This is the part worth reviewing, because each one is a thing we could have quietly implied instead:

• Self-hosted servers. The code supports Jellyfin, Navidrome/Subsonic and Plex, and the Flatpak has the network permission they need. Nobody has signed in to a real server from the installed package and played a track. So the page says so plainly and invites reports either way, rather than listing three provider names and hoping.
• Sound reaching a speaker. Build machines have no audio device. Decode, timing, seeking and transport are real; the last hop is a manual check.
• The file chooser dialog. What is automated is everything after the click.
• Stored credentials surviving a restart in the Flatpak.
• MPRIS from the packaged app. It works in the native Linux build and the package declares the names, but media keys against the installed Flatpak have not been confirmed.
• Notifications, since nothing posts one, which is why no permission is requested for it.

The sandbox section

Written for someone deciding whether to trust the app, not for a packager. It covers what "no filesystem permission at all" means in practice, that an unreachable folder produces a recoverable error and keeps the indexed tracks rather than overwriting the library with an empty one, and how to inspect and revoke grants (flatpak info --show-permissions, flatpak documents, flatpak document-unexport).

It is also honest that the network permission is general rather than scoped to particular hosts, because a self-hosted server can be anywhere.

Bug reporting

Points at the in-app secret-free reporter (Settings → Report a bug) rather than restating it, lists the four things that actually help diagnose a Linux problem, and names what not to paste: server URLs, usernames, tokens, and full paths containing a username. A GitHub issue is public and permanent.

Deliberately not in this PR

The AppStream <release> description. #454 mentions it, but the metainfo is currently being edited by #614 and #623, and the version that will carry the first Flathub release is not picked yet. Adding release-entry prose here would conflict for no benefit. The two are consistent: neither claims streaming.

What was validated

• every one of the seven internal links resolves against main, checked rather than assumed
• scripts/check_secrets.sh clean, which matters more than usual for a page that talks about what not to paste
• no em dashes, per house style
• the "Audio output" settings path verified against lib/features/settings/playback/audio_output_settings_section.dart rather than guessed

🤖 Generated with Claude Code

https://claude.ai/code/session_01QLDN6yzLpSdXoFHYJNqyyp

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