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)

.env.example

@@ -64,3 +64,8 @@ OPENAI_API_KEY=
 PAYPAL_CLIENT_ID=
 PAYPAL_SECRET=
 PAYPAL_API=https://api-m.sandbox.paypal.com
+
+# Optional Redis — enables shared caching for rate limiting and site settings,
+# allowing horizontal scaling across multiple instances. Falls back to in-process
+# Maps when unset.
+REDIS_URL=redis://127.0.0.1:6379