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/lib/admin/guard.ts

@@ -40,6 +40,6 @@ export async function requireStaff(): Promise<StaffUser> {
 export async function requireStaffRateLimited(): Promise<StaffUser> {
   const staff = await requireStaff();
   const ip = await clientIp();
-  if (!rateLimit(`admin:${staff.id}:${ip}`, 30, 60_000).ok) redirect("/admin?error=ratelimit");
+  if (!(await rateLimit(`admin:${staff.id}:${ip}`, 30, 60_000)).ok) redirect("/admin?error=ratelimit");
   return staff;
 }