feat(src/window/pomodoro): implement Pomodoro timer widget and integrate it into the panel

Add Pomodoro component with UI controls and state management,
modify Panel to instantiate and cache Pomodoro and TodoList widgets,
hook datetime button to toggle Pomodoro and handle right‑click on todo list,
extend destroy logic to cleanly close Pomodoro and Todo instances.

src/window/controlcenter/main.py

@@ -43,6 +43,7 @@ class ModusControlCenter(AppletWindow):
             anchor="top right",
             margin="2px 10px 0px 0px",
             exclusivity="auto",
+            edge_margin=5,
             name="control-center-menu",
             visible=False,
             **kwargs,