refactor(agent-office): drop the random idle→break→idle cycle

The pixel-office game UI is gone, so simulating coffee-break /
nap / walk states no longer serves any purpose. Remove:
- scheduler's _check_idle_breaks job (no more 60s idle scan)
- BaseAgent.check_idle_break() and _break_until field
- 'break' from VALID_STATES and from transition() branches
- IDLE_BREAK_THRESHOLD / BREAK_DURATION_MIN / BREAK_DURATION_MAX
  config knobs
- 'idle/break' guard in each agent's on_schedule (now just 'idle')

Agents now sit in 'idle' between scheduled jobs and explicit
commands. Display reads 'Idle' instead of churning between idle
and break.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

agent-office/app/agents/insta.py

@@ -46,7 +46,7 @@ class InstaAgent(BaseAgent):
     async def on_schedule(self) -> None:
         """09:30 매일: 뉴스 수집 → 키워드 추출 → 텔레그램 후보 푸시.
         custom_config.auto_select=True면 카테고리당 1위 키워드 자동 슬레이트 생성."""
-        if self.state not in ("idle", "break"):
+        if self.state != "idle":
             return
         config = get_agent_config(self.agent_id) or {}
         custom = config.get("custom_config", {}) or {}