perf: improve event loop responsiveness

- avoid full state extraction for no-op subscriber broadcast frames
- coalesce queued mouse move events before dispatch
- cap idle pump waits while frame-sensitive work is active
- serialize AX-facing window position and size commits
- add focused tests for broadcast intent, mouse coalescing, and pump timing

Cap low-power event-loop waits, emit the post-swipe mouse refresh only
once, defer AX enhanced UI restore during animated frame commits, and
avoid hot-path allocation in mouse warp and scroll snap logic.