fix(ci): drop preserveModules from GXT-mode build for testem compat

`preserveModules: true` produced ~1000 per-source chunks in the GXT-mode
build output. testem-based Basic Test loads the static dist/ via Chrome
and waits for `testem.js` to be reachable from the page; with that many
script tags the cold-cache page load blew past the 120s
`browser_start_timeout`, producing "Browser failed to connect within
120s. testem.js not loaded?" with zero tests run.

The setting was added to support the GXT smoke harness. That harness
runs against Vite's dev server (`pnpm vite --port 5180`), not a built
dist, so the rollup build config is irrelevant to it. Dropping the
special case yields a single bundled chunk (~7.5MB / ~1.4MB gzipped)
that testem can load fast. Smoke harness path is unchanged.

Co-Authored-By: Claude Opus 4.7 (1M context) <[email protected]>

Author: lifeart

vite.config.mjs

@@ -34,24 +34,18 @@ export default defineConfig(({ mode }) => {
   // Use GXT_MODE=true to enable glimmer-next integration
   const useGxt = process.env.GXT_MODE === 'true';
 
-  // preserveModules + preserveEntrySignatures are required for the GXT test
-  // harness so test files can be served as independent modules; under the
-  // classic build those settings break vite's modulepreload-polyfill, so
-  // apply them only in GXT mode.
-  const build = useGxt
-    ? {
-        rollupOptions: {
-          preserveEntrySignatures: 'strict',
-          input: ['index.html'],
-          output: {
-            preserveModules: true,
-          },
-        },
-        minify: mode === 'production',
-      }
-    : {
-        minify: mode === 'production',
-      };
+  // preserveModules + preserveEntrySignatures previously emitted per-source
+  // chunks for the GXT smoke runner. That harness uses Vite's dev server
+  // (`pnpm vite --port 5180`) which serves modules natively, so the build-time
+  // preserveModules setting was no longer load-bearing — but it WAS load-
+  // breaking for the testem-based Basic Test job, which loads the static
+  // dist/ output: ~1000 script tags blew past testem's 120s
+  // `browser_start_timeout` waiting for them all to fetch+parse before
+  // testem.js could connect. Drop the special case so all builds emit a
+  // bundled output suitable for testem.
+  const build = {
+    minify: mode === 'production',
+  };
 
   return {
     plugins: [