Fix Upstash import path blocking server start (M5 QA).

rate-limit.ts imported from a non-existent interfaces/cache path; use infrastructure/cache so Playwright smoke can start the server.

src/interfaces/http/rate-limit.ts

@@ -1,7 +1,7 @@
 import { Ratelimit } from "@upstash/ratelimit";
 import { Redis } from "@upstash/redis";
 import type { NextFunction, Request, Response } from "express";
-import { isUpstashConfigured } from "../cache/upstash.js";
+import { isUpstashConfigured } from "../../infrastructure/cache/upstash.js";
 
 type RouteTier = "read" | "stream" | "write" | "health";