- UiElement: add Draggable flag; left-drag on a draggable element repositions
it as a floating window instead of starting a drag-drop sequence.
- UiRoot: add WantsMouse/WantsKeyboard properties (mirrors ImGui's WantCaptureMouse
pattern); add FindDraggable helper; inject _windowDragTarget state machine into
OnMouseDown/OnMouseMove/OnMouseUp so draggable windows track the pointer offset.
- UiNineSlicePanel: set Draggable=true so retail window frames are movable by default.
- GameWindow: OR _uiHost?.Root.WantsMouse|WantsKeyboard into the SilkMouseSource
wantCaptureMouse/wantCaptureKeyboard delegates and the direct MouseMove gate so
game actions (movement, world-pick) are suppressed while the pointer is over a
retail window — no double-handling with the InputDispatcher.
- GameWindow: wire all Silk Mice/Keyboards to UiHost after construction so the
UiRoot tree receives live input.
- Tests: 3 new UiRootInputTests covering WantsMouse hit-test, window-drag
reposition, and non-draggable panel immobility.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
