feat: Esc cancels active drag or new placement

### Summary
Escape key should cancel the active drag or new placement.

### Steps to Reproduce
1. Begin dragging a component (new or existing)
2. Press Esc

### Expected
- Dragging/placement is canceled and state is restored

### Actual
- Esc does not cancel the operation

### Acceptance Criteria
- Esc reliably aborts the drag/placement without committing changes
