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.

tests/test_spectrum_panel.py

@@ -4,9 +4,9 @@ from __future__ import annotations
 
 import math
 
-from somafm_tui import config
-from somafm_tui.spectrum import Frame, SpectrumEngine
-from somafm_tui.widgets.spectrum import (
+from beefy_player import config
+from beefy_player.spectrum import Frame, SpectrumEngine
+from beefy_player.widgets.spectrum import (
     VISUALIZER_LABELS,
     WATERFALL_HISTORY,
     SpectrumPanel,