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/rate-limit.test.ts

@@ -0,0 +1,47 @@
+import { beforeEach, describe, expect, it, vi } from "vitest";
+
+vi.mock("@/lib/redis", () => ({
+  redis: null,
+}));
+
+import { rateLimit } from "./rate-limit";
+
+beforeEach(() => {
+  vi.restoreAllMocks();
+});
+
+describe("rateLimit (in-memory fallback)", () => {
+  it("allows the first request", async () => {
+    const res = await rateLimit("test:1", 3, 60_000);
+    expect(res.ok).toBe(true);
+    expect(res.retryAfter).toBe(0);
+  });
+
+  it("allows up to the limit within a window", async () => {
+    const key = `test:2:${Date.now()}`;
+    expect((await rateLimit(key, 2, 60_000)).ok).toBe(true);
+    expect((await rateLimit(key, 2, 60_000)).ok).toBe(true);
+    const res = await rateLimit(key, 2, 60_000);
+    expect(res.ok).toBe(false);
+    expect(res.retryAfter).toBeGreaterThan(0);
+  });
+
+  it("resets after the window expires", async () => {
+    const key = `test:3:${Date.now()}`;
+    await rateLimit(key, 1, 50);
+    const res1 = await rateLimit(key, 1, 50);
+    expect(res1.ok).toBe(false);
+    await new Promise((r) => setTimeout(r, 60));
+    const res2 = await rateLimit(key, 1, 50);
+    expect(res2.ok).toBe(true);
+  });
+
+  it("uses separate keys independently", async () => {
+    const a = await rateLimit("key-a", 1, 60_000);
+    const b = await rateLimit("key-b", 1, 60_000);
+    expect(a.ok).toBe(true);
+    expect(b.ok).toBe(true);
+    const a2 = await rateLimit("key-a", 1, 60_000);
+    expect(a2.ok).toBe(false);
+  });
+});