feat(task-watcher): main.py + Dockerfile + requirements + env (SP-10)

FastAPI lifespan에서 watcher_loop 스폰. /health. tzdata(zoneinfo Asia/Seoul).
.env: REDIS_URL, STOCK_BASE_URL, TRADING_START/END.
Plan-B-Infra Phase 2.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

services/task-watcher/main.py

@@ -0,0 +1,36 @@
+"""task-watcher FastAPI entry — health + lifespan (watcher loop spawn)."""
+from __future__ import annotations
+
+import asyncio
+import logging
+from contextlib import asynccontextmanager
+
+from fastapi import FastAPI
+
+import watcher
+
+logging.basicConfig(level=logging.INFO, format="%(asctime)s %(name)s %(levelname)s %(message)s")
+logger = logging.getLogger(__name__)
+
+
+@asynccontextmanager
+async def lifespan(app: FastAPI):
+    watcher_task = asyncio.create_task(watcher.watcher_loop())
+    logger.info("task-watcher lifespan 시작")
+    try:
+        yield
+    finally:
+        watcher_task.cancel()
+        try:
+            await watcher_task
+        except asyncio.CancelledError:
+            pass
+        logger.info("task-watcher lifespan 종료")
+
+
+app = FastAPI(lifespan=lifespan)
+
+
+@app.get("/health")
+def health():
+    return {"ok": True, "service": "task-watcher"}