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_timezone.py

@@ -5,7 +5,7 @@ from pathlib import Path
 
 import pytest
 
-from somafm_tui.widgets import common
+from beefy_player.widgets import common
 
 BERLIN = Path("/usr/share/zoneinfo/Europe/Berlin")
 UTC_FILE = Path("/usr/share/zoneinfo/UTC")