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/stock.py

@@ -44,7 +44,7 @@ class StockAgent(BaseAgent):
     display_name = "주식 트레이더"
 
     async def on_schedule(self) -> None:
-        if self.state not in ("idle", "break"):
+        if self.state != "idle":
             return
 
         task_id = create_task(self.agent_id, "news_summary", {"limit": 15})
@@ -129,7 +129,7 @@ class StockAgent(BaseAgent):
           4) status=='success' → telegram_payload.text 를 parse_mode 그대로 전송
           5) 예외/실패 → 운영자에게 별도 텔레그램 알림 (HTML)
         """
-        if self.state not in ("idle", "break"):
+        if self.state != "idle":
             return
 
         task_id = create_task(self.agent_id, "screener_run", {"mode": "auto"})
@@ -243,7 +243,7 @@ class StockAgent(BaseAgent):
           4) failures > 30% → 경고 알림 후 메인 메시지 발송
           5) 정상 → Top 5 호재/악재 메시지 발송 (MarkdownV2)
         """
-        if self.state not in ("idle", "break"):
+        if self.state != "idle":
             return
 
         task_id = create_task(self.agent_id, "ai_news_sentiment", {})