feat: D&D SRD 5.2 API — FastAPI app with flat JSON caching

- Data fetched from Open5e API: 3,215 items (339 spells, 330 creatures,
  24 classes, 2,319 magic items, 203 equipment)
- FastAPI app with API key auth (X-API-Key header or ?api_key= param)
- Sliding window rate limiting (60 req/min, 10K req/day)
- Dice rolling endpoint (e.g., /api/dice/roll?spec=2d20+5)
- Full-text search across all resource types
- Pagination, filtering (name, level, school, class, etc.)
- Admin CLI for API key management
- nginx + systemd service ready for deployment

requirements.txt

@@ -0,0 +1,2 @@
+fastapi>=0.100.0
+uvicorn[standard]>=0.20.0