A step opens a tab the way a person has to, through the menu when it is hidden

CI run 35 was red: the suite died after step 15 with `widget with text
"Container" not found`. Nothing in the editor broke — the tenth tab (#73) pushed
Container behind the `»` button at the test window's 1280 px, exactly the case
#84 was built for, and three steps still clicked the tab name directly.

openTab(t, tab) in tools/e2e/lib/scaffold.mjs asks tabRow() whether the tab is
hidden and goes through the menu when it is, so the fix lives in one place rather
than in every step that opens a tab. The LABELS record moves there as TAB_LABELS,
since both the helper and 14-overflow need it.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

tools/e2e/lib/scaffold.mjs

@@ -100,3 +100,32 @@ export async function scaffoldBehavior(t, options) {
     },
   };
 }
+
+/** What each tab button reads – the text a check has to click to open it. */
+export const TAB_LABELS = {
+  scene: 'Scene',
+  game: 'Game',
+  graph: 'Behavior',
+  statemachine: 'State machine',
+  shader: 'Shader',
+  texture: 'Texture',
+  animation: 'Animation',
+  container: 'Container',
+  list: 'List',
+  particles: 'Particles',
+};
+
+/**
+ * Opens a tab by clicking it, through the `»` menu when the row had to hide it. Since the tenth tab
+ * (#73) that is the normal case at the test window's width: a plain `clickText('Container')` found
+ * nothing and took the whole suite down with it.
+ */
+export async function openTab(t, tab) {
+  const row = await t.json('__gm.tabRow()');
+  if (row.hidden.includes(tab)) {
+    await t.clickText('»');
+    await t.sleep(300);
+  }
+  await t.clickText(TAB_LABELS[tab]);
+  await t.sleep(400);
+}