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)

src/app/api/client/sso/route.ts

@@ -16,7 +16,7 @@ export async function GET() {
   const userId = Number(session.user.id);
 
   // Throttle SSO ticket generation (5 per 30s per user) — prevent ticket spam.
-  if (!rateLimit(`sso:${userId}`, 5, 30_000).ok) {
+  if (!(await rateLimit(`sso:${userId}`, 5, 30_000)).ok) {
     return new Response(JSON.stringify({ error: "Rate limited" }), { status: 429 });
   }