fix(@angular/build): serve HTML files directly

Ensure direct requests to HTML files result in them being served.

Closes #28063

(cherry picked from commit 11a140b)

packages/angular/build/src/tools/vite/middlewares/index-html-middleware.ts

@@ -6,6 +6,7 @@
  * found in the LICENSE file at https://angular.dev/license
  */
 
+import { extname } from 'node:path';
 import type { Connect, ViteDevServer } from 'vite';
 import {
   AngularMemoryOutputFiles,
@@ -28,13 +29,14 @@ export function createAngularIndexHtmlMiddleware(
     // Parse the incoming request.
     // The base of the URL is unused but required to parse the URL.
     const pathname = pathnameWithoutBasePath(req.url, server.config.base);
-    if (pathname !== '/' && pathname !== '/index.html') {
+    const extension = extname(pathname);
+    if (extension !== '.html') {
       next();
 
       return;
     }
 
-    const rawHtml = outputFiles.get('/index.html')?.contents;
+    const rawHtml = outputFiles.get(pathname)?.contents;
     if (!rawHtml) {
       next();