perf: add bans.user_id index, Redis cache layer, rate-limit improvements, radio contest/giveaway columns, and tests

- Add DB index on bans.user_id to speed up per-request ban lookups (migration 0008)
- Replace in-process rate limiter with Redis-backed implementation with in-memory fallback
- Add Redis caching layer for site settings with TTL invalidation (migration 0009)
- Add rate limiting to resetPassword to prevent token brute-force attacks
- Update all rateLimit callers to await the now-async function
- Flesh out RadioContests and RadioGiveaways models with title, description, prize, date, and winner columns
- Update radio contest/giveaway pages to display new fields
- Add tests for rate limiter (4 tests) and password-reset actions (3 tests)
- Add REDIS_URL environment variable (optional, falls back to in-memory)

package.json

@@ -23,6 +23,7 @@
     "bcryptjs": "^3.0.2",
     "croner": "^10.0.1",
     "hash-wasm": "^4.12.0",
+    "ioredis": "^5.11.1",
     "jszip": "^3.10.1",
     "lucide-react": "^1.23.0",
     "next": "^16.2.10",