fix: Sitemap resource loading issue (#4042)

## Description

1. What is this PR about (link the issue and add a short description)

## Steps for reproduction

1. click button
2. expect xyz

## Code Review

- [ ] hi @kof, I need you to do
  - conceptual review (architecture, feature-correctness)
  - detailed review (read every line)
  - test it on preview

## Before requesting a review

- [ ] made a self-review
- [ ] added inline comments where things may be not obvious (the "why",
not "what")

## Before merging

- [ ] tested locally and on preview environment (preview dev login:
5de6)
- [ ] updated [test
cases](https://github.com/webstudio-is/webstudio/blob/main/apps/builder/docs/test-cases.md)
document
- [ ] added tests
- [ ] if any new env variables are added, added them to `.env` file

apps/builder/app/shared/$resources/sitemap.xml.server.ts

@@ -2,6 +2,8 @@ import { json } from "@remix-run/server-runtime";
 import { prisma } from "@webstudio-is/prisma-client";
 import { parsePages } from "@webstudio-is/project-build/index.server";
 import { getStaticSiteMapXml } from "@webstudio-is/sdk";
+import { parseBuilderUrl } from "../router-utils/origins";
+import { isBuilder } from "../router-utils";
 
 /**
  * This should be a route in SvelteKit, as it can be fetched server-side without an actual HTTP request.
@@ -10,24 +12,16 @@ import { getStaticSiteMapXml } from "@webstudio-is/sdk";
  * Note: We are not moving this to routes to avoid generating an additional 30MB function on deploy.
  */
 export const loader = async ({ request }: { request: Request }) => {
-  const referer = request.headers.get("referer");
-
-  if (referer == null) {
-    throw json({ message: "No referer" }, { status: 400 });
+  if (isBuilder(request) === false) {
+    throw new Error("Only builder requests are allowed");
   }
 
-  const segments = new URL(referer).pathname.slice(1).split("/");
-
-  if (segments.length !== 2) {
-    throw json({ message: "Invalid referer" }, { status: 400 });
-  }
+  const { projectId } = parseBuilderUrl(request.url);
 
-  if (segments[0] !== "builder") {
-    throw json({ message: "Invalid referer" }, { status: 400 });
+  if (projectId === undefined) {
+    throw new Error("projectId is required");
   }
 
-  const projectId = segments[1];
-
   // get pages from the database
   const build = await prisma.build.findFirst({
     where: {