perf(office-ui): stop per-token full-tree renders, sleep hidden Phaser loop, cut broadcast churn

Company-mode UIs became unusably slow once work items and transcripts
grew. Three presentation-layer fixes, none touching work progression:

- App.tsx: buffer assistant_delta/thinking_delta store writes per task
  and flush every 80ms instead of once per token; any non-delta event
  for the same task flushes first so draft/clearDraft ordering is
  byte-identical. The unconditional per-event setUiTick (whole-app
  re-render per websocket event) is now a 300ms trailing throttle.
- PhaserGame: display:none does not stop requestAnimationFrame, so the
  office scene kept burning CPU on every other page. The loop now
  sleeps when the office page is hidden and wakes (with a parent-bounds
  refresh) on return; bridge writes stay synchronous so no state is lost.
- Kanban collab_sync debounce 0.2s -> 1.5s: the broadcaster is a
  trailing coalescer, so the final board state still always ships; each
  fire is a full-project snapshot build, which at 5/s dominated backend
  CPU on large projects. CommsPanel poll 8s -> 30s (comms_state_dirty
  push already drives freshness) and its interval no longer pins a
  stale onRefresh closure.

Verified: tsc + vite build, App.test.tsx / workItemSessions structural
tests, backend suites (company_review_flow incl. debounce push test,
kanban_push_runtime, actor_runtime_company_mode, task_mode_contract,
work_item_transition — 119 green), and canvas_smoke e2e against a real
server with zero console errors.

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

opc/layer2_organization/company_mode.py

@@ -1391,7 +1391,12 @@ class CompanyWorkItemExecutor:
         # and a single background coroutine coalesces + broadcasts.
         self._kanban_dirty = False
         self._kanban_broadcast_task = None
-        self._kanban_debounce_sec: float = 0.2
+        # Trailing debounce: the broadcaster always fires once more after the
+        # last dirty mark, so the final board state is never lost. Each fire
+        # runs a full build_collab_sync (whole-project snapshot), which is
+        # expensive on large projects — keep the window generous. UI-only;
+        # the state machine never waits on this broadcast.
+        self._kanban_debounce_sec: float = 1.5
         self._runtime_invariant_issue_keys = set()
         self.runtime = CompanyRuntime(
             org_engine=org_engine,