feat(web): add Cloudflare Worker server entry with scheduled reminders

Sets up the server handler using TanStack React Start and implements
a scheduled event handler to run reminder tasks via Cloudflare cron triggers.

apps/web/src/server.ts

@@ -0,0 +1,18 @@
+import { runSendReminders } from "@kk/api/routers/index";
+import {
+	createStartHandler,
+	defaultStreamHandler,
+} from "@tanstack/react-start/server";
+
+const fetch = createStartHandler(defaultStreamHandler);
+
+export default {
+	fetch,
+	async scheduled(
+		_event: { cron: string; scheduledTime: number },
+		_env: Record<string, unknown>,
+		ctx: { waitUntil: (promise: Promise<unknown>) => void },
+	) {
+		ctx.waitUntil(runSendReminders());
+	},
+};