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.

stock/app/screener/__init__.py

@@ -0,0 +1,12 @@
+"""Stock screener — KRX 강세주 분석 노드 기반 보드.
+
+See docs/superpowers/specs/2026-05-12-stock-screener-board-design.md
+"""
+
+from .engine import Screener, ScreenContext, ScreenerResult
+from .registry import NODE_REGISTRY, GATE_REGISTRY
+
+__all__ = [
+    "Screener", "ScreenContext", "ScreenerResult",
+    "NODE_REGISTRY", "GATE_REGISTRY",
+]