refactor!: rename somafm-tui to beefy-player

The app is now a general internet-radio player rather than a SomaFM client, so the package, console script, MPRIS identity, mpv namespaces, macOS tap names, XDG directories and docs all move to beefy-player.

Environment variables are now BEEFY_* (the old SOMAFM_* spellings are still honoured) and an existing ~/.config/somafm-tui/config.json is migrated on first run, so favourites and volume survive the rename.

The visible interface is untouched: same layout, same logo, same keys.

beefy_player/mediasession.py

@@ -0,0 +1,160 @@
+"""Desktop media integration, with a platform-neutral face.
+
+The rest of the app only ever talks to this small surface::
+
+    session = create_media_session(actions, enabled=True)
+    session.start()
+    session.set_track(station=…, title=…, artist=…, album=…, art_url=…)
+    session.set_status("Playing")
+    session.set_volume(0.7)
+
+which keeps the platform differences in one place:
+
+* **Linux / BSD / any D-Bus desktop** — :class:`beefy_player.mpris.MprisService`
+  exports ``org.mpris.MediaPlayer2.beefyplayer.instance<pid>`` on the session
+  bus, so GNOME/KDE widgets, lock screens and ``playerctl`` show the station
+  and can drive playback.
+* **macOS** — mpv *is* the app the system knows about: its Cocoa backend
+  registers with ``MPRemoteCommandCenter``/``MPNowPlayingInfoCenter``, which
+  is what Control Center, the menu bar and the media keys talk to.  So there
+  is nothing to publish here, and the media keys are routed back into the TUI
+  by mpv (see :mod:`beefy_player.player`).  :class:`NowPlayingSession` only
+  keeps the state the status bar renders and stays out of the way.
+
+Anything else (or a disabled/absent backend) degrades to an inert session
+whose status label is ``off`` — the TUI carries on regardless.
+"""
+
+from __future__ import annotations
+
+import sys
+from queue import Queue
+from typing import Any
+
+__all__ = [
+    "MediaSession",
+    "NowPlayingSession",
+    "create_media_session",
+    "media_actions_queue",
+]
+
+
+def media_actions_queue() -> Queue[str]:
+    """Queue of commands coming back from the desktop media integration."""
+    return Queue()
+
+
+class MediaSession:
+    """Inert media session: keeps state, publishes nothing.
+
+    Used as the base for backends that have no IPC service of their own and as
+    the fallback when desktop integration is unavailable.
+    """
+
+    #: Short name for the status bar ("mpris", "nowplaying", …).
+    label = "media"
+
+    def __init__(self, actions: Queue[str], *, enabled: bool = True) -> None:
+        self.actions = actions
+        self.enabled = bool(enabled)
+        self.available = False
+        self.error = ""
+        self._status = "Stopped"
+        self._volume = 0.7
+        self._metadata: dict[str, Any] = {}
+
+    # ----- lifecycle ---------------------------------------------------- #
+
+    def start(self) -> None:
+        return None
+
+    def stop(self) -> None:
+        return None
+
+    # ----- state -------------------------------------------------------- #
+
+    @property
+    def status_label(self) -> str:
+        if not self.enabled:
+            return "off"
+        if self.available:
+            return "on"
+        return "error" if self.error else "off"
+
+    def set_status(self, status: str) -> None:
+        if status in ("Playing", "Paused", "Stopped"):
+            self._status = status
+
+    def set_volume(self, ratio: float) -> None:
+        self._volume = max(0.0, min(1.0, float(ratio)))
+
+    def set_track(
+        self,
+        *,
+        station: str,
+        title: str,
+        artist: str,
+        album: str = "",
+        art_url: str = "",
+        stream_url: str = "",
+        track_key: str = "",
+    ) -> None:
+        self._metadata = {
+            "station": station,
+            "title": title,
+            "artist": artist,
+            "album": album,
+            "art_url": art_url,
+            "stream_url": stream_url,
+            "track_key": track_key,
+        }
+
+
+class NowPlayingSession(MediaSession):
+    """macOS: mpv owns the system Now Playing session, we just mirror state.
+
+    mpv's Cocoa backend publishes the live ICY title (and play/pause state) to
+    Control Center and receives the media keys; :mod:`beefy_player.player` routes
+    those key presses back into this app.  ``available`` is false when the audio
+    backend is not mpv, because then nobody publishes anything.
+    """
+
+    label = "nowplaying"
+
+    def __init__(
+        self,
+        actions: Queue[str],
+        *,
+        enabled: bool = True,
+        backend: str | None = "mpv",
+    ) -> None:
+        super().__init__(actions, enabled=enabled)
+        self.backend = backend
+        self.available = bool(enabled) and backend == "mpv"
+
+    @property
+    def status_label(self) -> str:
+        if not self.enabled:
+            return "off"
+        return "on" if self.available else "off"
+
+
+def create_media_session(
+    actions: Queue[str],
+    *,
+    enabled: bool = True,
+    backend: str | None = None,
+    platform: str | None = None,
+) -> MediaSession:
+    """Pick the right desktop media backend for this platform.
+
+    ``platform``/``backend`` exist so the choice is testable without touching
+    the real machine.
+    """
+    system = sys.platform if platform is None else platform
+    if system == "darwin":
+        return NowPlayingSession(actions, enabled=enabled, backend=backend)
+
+    from .mpris import MprisService
+
+    return MprisService(actions, enabled=enabled)