feat(#27): Gate B [07/10]: FastAPI health endpoint + app factory (H-1)

- App factory pattern (FUND-8): create_app() produces fresh app per test
- Logging config (structured, no secrets)
- Config validation: SLAB_AES_KEY required, WOO_BASE_URL HTTPS-only
- GET /api/health returns 200 {status: ok, version, woo_reachable: false}
- SQLite + alembic skeleton: full DATA-MODEL schema, initial migration
- API contract tests via httpx TestClient: 5 cases all green
  - test_returns_200, test_returns_ok_status, test_woo_reachable_false
  - test_response_shape, test_with_test_client_lifespan (FUND-9/10)

backend/Dockerfile

@@ -0,0 +1,21 @@
+FROM python:3.13-slim
+
+WORKDIR /app
+
+COPY backend/requirements.txt .
+RUN pip install --no-cache-dir -r requirements.txt
+
+COPY backend/ .
+
+# Create data and images directories
+RUN mkdir -p /data /images /app/prompts
+
+# Bind mount for prompts (read-only)
+# Volumes for data and images are handled by docker-compose
+
+ENV PYTHONUNBUFFERED=1
+ENV PYTHONDONTWRITEBYTECODE=1
+
+EXPOSE 8000
+
+CMD ["uvicorn", "app.main:create_app", "--factory", "--host", "0.0.0.0", "--port", "8000"]