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

docker-compose.yml

@@ -108,6 +108,32 @@ services:
       timeout: 5s
       retries: 3
 
+  agent-office:
+    build:
+      context: ./agent-office
+    container_name: agent-office
+    restart: unless-stopped
+    ports:
+      - "18900:8000"
+    environment:
+      - TZ=${TZ:-Asia/Seoul}
+      - CORS_ALLOW_ORIGINS=${CORS_ALLOW_ORIGINS:-http://localhost:3007,http://localhost:8080}
+      - STOCK_LAB_URL=http://stock-lab:8000
+      - MUSIC_LAB_URL=http://music-lab:8000
+      - TELEGRAM_BOT_TOKEN=${TELEGRAM_BOT_TOKEN:-}
+      - TELEGRAM_CHAT_ID=${TELEGRAM_CHAT_ID:-}
+      - TELEGRAM_WEBHOOK_URL=${TELEGRAM_WEBHOOK_URL:-}
+    volumes:
+      - ${RUNTIME_PATH:-.}/data/agent-office:/app/data
+    depends_on:
+      - stock-lab
+      - music-lab
+    healthcheck:
+      test: ["CMD", "python", "-c", "import urllib.request; urllib.request.urlopen('http://localhost:8000/health')"]
+      interval: 30s
+      timeout: 5s
+      retries: 3
+
   travel-proxy:
     build: ./travel-proxy
     container_name: travel-proxy