refactor: extract reusable utils, remove screencapture facade

- Add ManagedTimer to replace repeated source_remove/timeout_add boilerplate
- Add EvdevLockService base class for numlock/capslock (cut 154→28 lines)
- Add BaseNotchIndicator for 5 near-identical indicator classes (cut 404→171 lines)
- Add load_pixbuf_thumbnail and resolve_monitor to utils
- Delete screencapture.py facade; callers use Screenshot/ScreenRecorder directly

src/services/modus.py

@@ -37,12 +37,6 @@ def __getattr__(name):
             _inst = None
         setattr(mod, name, _inst)
         return _inst
-    if name == "screen_capture_service":
-        from services.screencapture import ScreenCapture
-
-        _inst = ScreenCapture()
-        setattr(mod, name, _inst)
-        return _inst
     if name == "screenshot_service":
         from services.screenshot import Screenshot