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/search.py

@@ -0,0 +1,14 @@
+"""Filter input (hidden until you press /)."""
+
+from __future__ import annotations
+
+from textual.widgets import Input
+
+
+class SearchInput(Input):
+    def __init__(self) -> None:
+        super().__init__(
+            placeholder="filter stations…  (enter tune · esc close)",
+            id="search",
+            disabled=True,
+        )