fix(release-gate): map index.html to the UI impact domain

Unblock Core+Impact selection for H5 shell title changes.

Co-authored-by: Cursor <cursoragent@cursor.com>

release-gate/impact.test.mjs

@@ -17,6 +17,17 @@ test('docs-only changes use the compact core gate', async () => {
   assert.equal(selection.unmapped_paths.length, 0);
 });
 
+test('H5 shell index.html maps to the UI domain', async () => {
+  const catalog = await loadScenarioCatalog();
+  const selection = selectImpactScenarios({
+    catalog,
+    changedPaths: ['index.html'],
+  });
+  assert.equal(selection.strategy, 'impact');
+  assert.deepEqual(selection.impact_groups, ['UI']);
+  assert.equal(selection.unmapped_paths.length, 0);
+});
+
 test('domain changes select the domain and dependency closure', async () => {
   const catalog = await loadScenarioCatalog();
   const selection = selectImpactScenarios({