feat: Agent Office — AI 에이전트 가상 오피스 (#2)

## Summary
- 2D 픽셀아트 가상 오피스에서 AI 에이전트(Stock, Music)가 실제 작업 수행
- FastAPI + WebSocket 실시간 상태 동기화 + 텔레그램 봇 양방향 알림/승인
- BaseAgent FSM (idle/working/waiting/reporting/break), 서비스 프록시 패턴
- Docker Compose 서비스 (port 18900) + Nginx WebSocket 프록시

## Changes (13 commits)
- Backend scaffold: config, db, models, Dockerfile
- WebSocket manager + Service proxy
- BaseAgent FSM + StockAgent + MusicAgent
- Telegram bot + Scheduler
- FastAPI main (REST + WS endpoints)
- Infrastructure: docker-compose + nginx
- Code review fixes: HTTPException, async polling, input validation

Reviewed-on: #2

agent-office/app/config.py

@@ -0,0 +1,23 @@
+import os
+
+# Service URLs (Docker internal network)
+STOCK_LAB_URL = os.getenv("STOCK_LAB_URL", "http://localhost:18500")
+MUSIC_LAB_URL = os.getenv("MUSIC_LAB_URL", "http://localhost:18600")
+
+# Telegram
+TELEGRAM_BOT_TOKEN = os.getenv("TELEGRAM_BOT_TOKEN", "")
+TELEGRAM_CHAT_ID = os.getenv("TELEGRAM_CHAT_ID", "")
+TELEGRAM_WEBHOOK_URL = os.getenv("TELEGRAM_WEBHOOK_URL", "")
+
+# Database
+DB_PATH = os.getenv("AGENT_OFFICE_DB_PATH", "/app/data/agent_office.db")
+
+# CORS
+CORS_ALLOW_ORIGINS = os.getenv(
+    "CORS_ALLOW_ORIGINS", "http://localhost:3007,http://localhost:8080"
+)
+
+# Idle break threshold (seconds)
+IDLE_BREAK_THRESHOLD = int(os.getenv("IDLE_BREAK_THRESHOLD", "300"))  # 5 min
+BREAK_DURATION_MIN = int(os.getenv("BREAK_DURATION_MIN", "60"))       # 1 min
+BREAK_DURATION_MAX = int(os.getenv("BREAK_DURATION_MAX", "180"))      # 3 min