Add Unix socket API for OS-wide keyboard shortcuts

Implement single binary pattern where cm-player acts as both server
(TUI mode) and client (command sender) based on CLI arguments.

- Add Unix socket API server at $XDG_RUNTIME_DIR/cm-player.sock
- Add client mode for sending commands: cm-player play-pause, next, etc.
- Support all playback commands: play-pause, stop, next, prev
- Support volume commands: volume-up, volume-down, volume <0-100>
- Support seek commands: seek-forward, seek-backward
- Support status query and quit commands
- Add short command aliases (pp, n, p, vu, vd, sf, sb, s, q)
- Commands run in parallel thread, non-blocking main loop
- Enable OS-wide keyboard shortcut integration (XF86Audio* keys)

Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name = "cm-player"
-version = "0.1.24"
+version = "0.1.25"
 edition = "2021"
 
 [dependencies]