feat(listen-together): listen in sync with friends in Metrolist-compatible rooms

[maxrave-dev]

Listen Together: create a room, share an 8-character code, and everyone hears the same track at the same position.

The rooms are the ones Metrolist already uses, so a SimpMusic client and a Metrolist client can sit in the same room. The protocol work is in the core submodule — see maxrave-dev/core#28, which must merge first.

What a user sees

• Entry point in the Home and Library top bars, carrying a dot while a room is live.
• Host creates a room; guests join by code, with approval unless auto-approve is on.
• Host controls playback for the room. Guests may pause locally and stay paused — pressing play asks the server where the room is now and rejoins there, rather than resuming where this device happened to stop.
• Settings: server choice, auto-approve joins, and a client-side blocklist.

Screen

Built as a page rather than a stack of identical cards: two columns once the window is wide enough for two real ones, with the room code as the one deliberately outsized element — it is the thing people read aloud. Connection state is a single line, members are a divided list, and leaving/settings are quiet Material buttons at the end.

Everything resolves through MaterialTheme.colorScheme, so it is correct on the light theme too. The screens the glass treatment was borrowed from (Album, Playlist, Artist, Analytics) all sit inside ForceDarkContent, so their white default tint is always over a dark page; this one follows the theme and has to pass its own.

Architecture

composeApp never sees the protocol. It talks to ListenTogetherRepository in domain; ListenTogetherRepositoryImpl in data is the only place that knows the service module exists.

Notes

• Crossfade is suppressed inside a room (a fade overlaps two tracks for seconds and drifts the room apart). The user's setting is untouched — it is a separate override on the player, the same shape as the sleep-timer fade.
• docs/ is removed in this branch.
• version-name is bumped to 2.0.0-alpha, which the Windows MSI target rejects — desktopApp/build.gradle.kts only strips a -hf suffix today, so it needs substringBefore("-") before a desktop release build will configure.

Testing

Protocol round-trip and handshake tests live in core. Playback sync was exercised with two live clients against wss://metroserverx.meowery.eu/ws.