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/widgets/help.py

@@ -0,0 +1,97 @@
+"""Full-screen keyboard help."""
+
+from __future__ import annotations
+
+import sys
+import textwrap
+
+from rich.console import Group
+from rich.table import Table
+from rich.text import Text
+from textual.app import ComposeResult
+from textual.screen import ModalScreen
+from textual.widgets import Static
+
+from .common import SPECTRUM_STOPS, gradient
+
+HELP_ROWS: tuple[tuple[str, str], ...] = (
+    ("↑ / ↓  j / k", "move through the station list"),
+    ("enter", "tune in to the selected station"),
+    ("space", "play / pause the current station"),
+    ("s", "stop playback"),
+    ("] / [", "next / previous station (tunes immediately)"),
+    ("+ / -", "volume up / down"),
+    ("m", "mute / unmute"),
+    ("f", "favourite — favourites float to the top"),
+    ("/", "filter stations by title, genre or description"),
+    ("esc", "clear the filter / close overlays"),
+    (
+        "v",
+        "cycle visualiser: mirror → bars → wave → waterfall → radial → braille",
+    ),
+    ("r", "refresh station list and song history"),
+    ("g / G", "jump to the top / bottom of the list"),
+    ("? ", "this help"),
+    ("q", "quit"),
+)
+
+ABOUT_COMMON = (
+    (
+        "Stations and song history come from somafm.com "
+        "(channels.json + songs/<station>.json)."
+    ),
+)
+
+ABOUT_LINUX = (
+    (
+        "The spectrum captures your actual PulseAudio/PipeWire output with "
+        "parec (SYNC); otherwise it falls back to a muted ffmpeg stream tap "
+        "(FFT, can drift) or a synthesized display (SIM)."
+    ),
+    (
+        "The desktop picks us up over MPRIS as a "
+        "somafmtui media player — try `playerctl -l` / `playerctl metadata`."
+    ),
+)
+
+ABOUT_MACOS = (
+    (
+        "The spectrum captures your Mac's real audio output (SYNC) with a "
+        "native Core Audio process tap — nothing to install. macOS asks for "
+        "System Audio Recording permission the first time; without it the "
+        "analyser falls back to a muted ffmpeg stream tap (FFT, can drift) "
+        "or a synthesized display (SIM)."
+    ),
+    (
+        "mpv publishes what is playing to the macOS Now Playing session, so "
+        "Control Center and the keyboard media keys control this app."
+    ),
+)
+
+ABOUT = ABOUT_COMMON + (ABOUT_MACOS if sys.platform == "darwin" else ABOUT_LINUX)
+
+
+class HelpScreen(ModalScreen[None]):
+    def compose(self) -> ComposeResult:
+        table = Table.grid(padding=(0, 2), expand=False)
+        table.add_column(style="bold cyan", no_wrap=True, justify="right")
+        table.add_column(style="")
+        for key, description in HELP_ROWS:
+            table.add_row(key, description)
+
+        header = Text()
+        header.append("◤ ", style=f"bold {gradient(SPECTRUM_STOPS, 0.9)}")
+        header.append("SOMAFM TUI", style=f"bold {gradient(SPECTRUM_STOPS, 0.55)}")
+        header.append("  keyboard & credits", style="dim")
+
+        footer = Text()
+        for paragraph in ABOUT:
+            for line in textwrap.wrap(paragraph, width=70):
+                footer.append(line + "\n", style="dim")
+
+        body = Group(header, Text(""), table, Text(""), footer)
+        yield Static(body, id="help")
+
+    def on_key(self, event) -> None:
+        event.stop()
+        self.dismiss(None)