Add callbacks support for all media actions

- Add CallbackConfig model for callback scripts
- Add callbacks section to config for optional command execution
- Add turn_on/turn_off/toggle endpoints (callback-only)
- Add callbacks for all media actions (play, pause, stop, next, previous, volume, mute, seek)
- Update README with callbacks documentation

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

config.example.yaml

@@ -44,4 +44,64 @@ scripts:
     label: "Restart"
     description: "Restart the PC immediately"
     timeout: 10
+    shell: true
+
+# Callback scripts (executed after media actions)
+# All callbacks are optional - if not defined, the action runs without callback
+callbacks:
+  # Media control callbacks (run after successful action)
+  on_play:
+    command: "echo Play triggered"
+    timeout: 10
+    shell: true
+
+  on_pause:
+    command: "echo Pause triggered"
+    timeout: 10
+    shell: true
+
+  on_stop:
+    command: "echo Stop triggered"
+    timeout: 10
+    shell: true
+
+  on_next:
+    command: "echo Next track"
+    timeout: 10
+    shell: true
+
+  on_previous:
+    command: "echo Previous track"
+    timeout: 10
+    shell: true
+
+  on_volume:
+    command: "echo Volume changed"
+    timeout: 10
+    shell: true
+
+  on_mute:
+    command: "echo Mute toggled"
+    timeout: 10
+    shell: true
+
+  on_seek:
+    command: "echo Seek triggered"
+    timeout: 10
+    shell: true
+
+  # Turn on/off/toggle (callback-only actions, no default behavior)
+  on_turn_on:
+    command: "echo Turn on callback"
+    timeout: 10
+    shell: true
+
+  on_turn_off:
+    command: "rundll32.exe user32.dll,LockWorkStation"
+    timeout: 5
+    shell: true
+
+  on_toggle:
+    command: "echo Toggle callback"
+    timeout: 10
     shell: true