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/env.ts

@@ -61,6 +61,8 @@ const schema = z.object({
   PAYPAL_CLIENT_ID: z.string().optional(),
   PAYPAL_SECRET: z.string().optional(),
   PAYPAL_API: z.string().url().optional(),
+  // Optional Redis — enables shared caching for rate limiting and site settings.
+  REDIS_URL: z.string().optional(),
 });
 
 type Env = z.infer<typeof schema>;