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

.gitignore

@@ -0,0 +1,38 @@
+# Dependencies
+node_modules/
+__pycache__/
+*.pyc
+venv/
+.venv/
+
+# Environment
+.env
+.env.local
+.env.*.local
+
+# Build
+.next/
+dist/
+build/
+out/
+frontend/dist/
+
+# IDE
+.idea/
+.vscode/
+*.swp
+*.swo
+
+# OS
+.DS_Store
+Thumbs.db
+
+# Logs
+*.log
+npm-debug.log*
+
+# Data (local dev)
+data/
+*.db
+*.sqlite
+backend/data/outputs/