Add a coffee break

Every so often a mug appears at the cat's nose, it sits down, dips its head in
and takes a few slow sips while steam rises. M01, optional stop.

The mug lives in its own click-through window like the chip, or inside the
overlay on Wayland. It goes away as soon as the cat is petted, dragged, sent to
sleep or moves on to something else, so no mug is ever left standing.

Also renames OverlayWindow's mode flag, which shadowed QWindow::active.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

qml/CatMoods.qml

@@ -5,7 +5,7 @@ import TNCat
 // Maps CatController::Mood onto the strings Cat.qml understands.
 QtObject {
     readonly property var names: ["walking", "running", "sitting", "grooming", "stretching",
-                                  "sleeping", "loving", "alert", "chasing", "batting"]
+                                  "sleeping", "loving", "alert", "chasing", "batting", "drinking"]
 
     function name(mood) {
         return names[mood] !== undefined ? names[mood] : "sitting"