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/Dockerfile

@@ -0,0 +1,16 @@
+FROM python:3.12-slim-bookworm
+ENV PYTHONUNBUFFERED=1
+
+WORKDIR /app
+
+RUN apt-get update && apt-get install -y --no-install-recommends \
+    ca-certificates tzdata \
+ && rm -rf /var/lib/apt/lists/*
+
+COPY requirements.txt .
+RUN pip install --no-cache-dir --timeout 600 --retries 5 -r requirements.txt
+
+COPY . .
+
+EXPOSE 8000
+CMD ["python", "-m", "uvicorn", "main:app", "--host", "0.0.0.0", "--port", "8000", "--workers", "1"]