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/redis.ts

@@ -0,0 +1,41 @@
+import Redis from "ioredis";
+
+const globalForRedis = globalThis as unknown as { redis?: Redis | null };
+
+function createRedis(): Redis | null {
+  const url = process.env.REDIS_URL;
+  if (!url) return null;
+  try {
+    const client = new Redis(url, {
+      maxRetriesPerRequest: 3,
+      retryStrategy(times) {
+        if (times > 3) return null;
+        return Math.min(times * 200, 2000);
+      },
+      lazyConnect: true,
+    });
+    client.on("error", () => {});
+    return client;
+  } catch {
+    return null;
+  }
+}
+
+export const redis: Redis | null =
+  globalForRedis.redis !== undefined
+    ? globalForRedis.redis
+    : (globalForRedis.redis = createRedis());
+
+export async function withRedis<T>(
+  fallback: () => Promise<T>,
+  redisFn: (client: Redis) => Promise<T>,
+): Promise<T> {
+  if (redis) {
+    try {
+      return await redisFn(redis);
+    } catch {
+      return fallback();
+    }
+  }
+  return fallback();
+}