Integrate IM channels and desktop agent office - #104

- Activity snapshots infer `responding` from token events (the default
  coding mode never emits it) and keep a bounded streaming tail plus each
  running tool's one-line call preview.
- The office controller overlays WebSocket token/reasoning events between
  snapshots (sequence-gated, throttled) without extra HTTP requests.
- Busy agents keep a status bubble (icon, verb, latest words or call
  preview) with priority-based collision avoidance; typing, reading,
  thinking and waiting have distinct motions.
- Members walk in from the door, collect a task envelope at their
  dispatcher's desk, and walk back to hand in a report before leaving;
  mesh messages fly as labelled envelopes. Reduced motion keeps the
  envelopes without walking.
- The page reports bubble rectangles so the Windows window region no
  longer clips bubbles above the walls.
- Add a macOS host: non-activating NSPanel with WKWebView, a
  chrome.webview shim, hit-test click-through, drag, resize, zoom and
  context menu. Not yet compiled on macOS.