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/.env.example

@@ -0,0 +1,11 @@
+# Plan-B-Infra — task-watcher
+
+# NAS Redis
+REDIS_URL=redis://192.168.45.54:6379
+
+# NAS stock holidays endpoint
+STOCK_BASE_URL=http://192.168.45.54:18500
+
+# 트레이딩 윈도우 (KST, HH:MM) — 이 시간대에만 queue:paused
+TRADING_START=07:00
+TRADING_END=16:30