refactor: rename stock-lab → stock (graduation)

- git mv stock-lab/ → stock/
- docker-compose.yml: 서비스 키 + container_name + build.context +
  frontend.depends_on + agent-office STOCK_LAB_URL → STOCK_URL
- agent-office/app: config.py, service_proxy.py, agents/stock.py, tests/
  STOCK_LAB_URL → STOCK_URL
- nginx/default.conf: proxy_pass http://stock-lab → http://stock (3 lines)
- CLAUDE.md / README.md / STATUS.md / scripts/ 문구 갱신
- stock/ 내부 자기 참조 갱신

lab 네이밍 정책 (feedback_lab_naming.md) graduation.
API URL / Python import / DB 파일명 변경 없음.

agent-office/app/config.py

@@ -1,7 +1,7 @@
 import os
 
 # Service URLs (Docker internal network)
-STOCK_LAB_URL = os.getenv("STOCK_LAB_URL", "http://localhost:18500")
+STOCK_URL = os.getenv("STOCK_URL", "http://localhost:18500")
 MUSIC_LAB_URL = os.getenv("MUSIC_LAB_URL", "http://localhost:18600")
 BLOG_LAB_URL = os.getenv("BLOG_LAB_URL", "http://localhost:18700")
 REALESTATE_LAB_URL = os.getenv("REALESTATE_LAB_URL", "http://localhost:18800")