fix(osd): show OSD at 100% via fabric-cli exec from keybinds

- Add osd_show_audio/osd_show_brightness methods on OSDWindow
- Register as standalone functions in __main__ for fabric-cli exec
- Keybinds now chain fabric-cli exec after wpctl/brightnessctl
- Emit brightness signal on threshold bypass for small changes

src/services/brightness.py

@@ -284,6 +284,7 @@ class Brightness(Service):
                 abs(new_percent - current_percent) < self.MIN_CHANGE_THRESHOLD
                 and self._last_raw != -1
             ):
+                self.emit("screen", new_percent)
                 return
 
             self._pending_raw = value