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.

shell.nix

@@ -1,6 +1,6 @@
 { pkgs ? import <nixpkgs> { } }:
 
-# FHS development shell for somafm-tui.
+# FHS development shell for beefy-player.
 #
 # Why FHS?  uv installs manylinux wheels from PyPI (notably NumPy) that expect
 # libstdc++.so.6 and friends in the usual FHS locations (/usr/lib, /lib).
@@ -12,13 +12,13 @@
 #   nix-shell            # enter the FHS shell
 #   rm -rf .venv         # once, if the venv was created by an older setup
 #   uv sync              # install Python deps with uv
-#   uv run somafm-tui    # start the radio
+#   uv run beefy-player  # start the radio
 #
 # Note: `nix-shell --run "..."` is not supported by FHS shell.nix files; enter
 # the shell interactively and run commands there.
 
 (pkgs.buildFHSEnv {
-  name = "somafm-tui";
+  name = "beefy-player";
 
   targetPkgs = pkgs: with pkgs; [
     # --- Python toolchain; uv owns all Python dependencies ---------------
@@ -83,13 +83,13 @@
       export DBUS_SESSION_BUS_ADDRESS="unix:path=$XDG_RUNTIME_DIR/bus"
     fi
 
-    export PS1='\[\e[1;35m\][somafm-tui]\[\e[0m\] \w \$ '
+    export PS1='\[\e[1;35m\][beefy-player]\[\e[0m\] \w \$ '
 
     echo ""
-    echo "  somafm-tui — FHS dev shell"
-    echo "  --------------------------"
+    echo "  beefy-player — FHS dev shell"
+    echo "  ----------------------------"
     echo "  uv sync            install / update python deps"
-    echo "  uv run somafm-tui  start the radio"
+    echo "  uv run beefy-player  start the radio"
     echo ""
     echo "  python : $(python3 --version 2>&1)"
     echo "  uv     : $(uv --version 2>&1)"