feat(01-01): Backend FastAPI skeleton + Docker build config

- FastAPI app with SPAStaticFiles catch-all (root_path NOT in constructor)
- config.py with DATA_PATH, PROMPTS_PATH, OUTPUTS_PATH, CAMPAIGNS_PATH, CONFIG_PATH
- Startup lifespan creates data directories automatically
- Health endpoint: GET /api/health -> {"status": "ok"}
- Dockerfile multi-stage: node:22-slim builds React, python:3.12-slim serves API+SPA
- --root-path /postgenerator set in Uvicorn CMD only (avoids Pitfall #4)
- docker-compose.yml: lab-postgenerator-app, proxy_net, named volume for data persistence
- requirements.txt with pinned versions: fastapi[standard]==0.135.1, anthropic==0.84.0

docker-compose.yml

@@ -0,0 +1,26 @@
+services:
+  app:
+    container_name: lab-postgenerator-app
+    build:
+      context: .
+      dockerfile: Dockerfile
+    env_file: .env
+    volumes:
+      - postgenerator-data:/app/data
+    networks:
+      - proxy_net
+    # NO exposed ports — traffic routed via lab-router nginx
+    deploy:
+      resources:
+        limits:
+          memory: 1024M
+          cpus: '1.0'
+    restart: unless-stopped
+
+volumes:
+  postgenerator-data:
+    name: postgenerator-data
+
+networks:
+  proxy_net:
+    external: true