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.py

@@ -5,8 +5,8 @@ from pathlib import Path
 
 import numpy as np
 
-from somafm_tui import spectrum as spectrum_module
-from somafm_tui.spectrum import Frame, SpectrumEngine
+from beefy_player import spectrum as spectrum_module
+from beefy_player.spectrum import Frame, SpectrumEngine
 
 PCM_SCRIPT = """#!/usr/bin/env python3
 import math, struct, sys, time
@@ -42,7 +42,7 @@ def tap_pcm(
 
 
 class FakeTap:
-    """Stand-in for ``somafm_tui.macos_tap.SystemAudioTap``."""
+    """Stand-in for ``beefy_player.macos_tap.SystemAudioTap``."""
 
     def __init__(
         self,