feat: add in-memory sliding window rate limiter

src/lib/server/rate-limit.ts

@@ -0,0 +1,33 @@
+export class RateLimiter {
+	private windows = new Map<string, number[]>();
+
+	constructor(
+		private maxRequests: number,
+		private windowMs: number
+	) {}
+
+	check(key: string): boolean {
+		const now = Date.now();
+		const timestamps = this.windows.get(key) ?? [];
+
+		const valid = timestamps.filter((t) => now - t < this.windowMs);
+
+		if (valid.length >= this.maxRequests) {
+			this.windows.set(key, valid);
+			return false;
+		}
+
+		valid.push(now);
+		this.windows.set(key, valid);
+		return true;
+	}
+
+	reset(key: string): void {
+		this.windows.delete(key);
+	}
+}
+
+export const loginLimiter = new RateLimiter(5, 15 * 60 * 1000);
+export const registrationLimiter = new RateLimiter(3, 60 * 60 * 1000);
+export const apiLimiter = new RateLimiter(60, 60 * 1000);
+export const nameGeneratorLimiter = new RateLimiter(10, 5 * 60 * 1000);