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/13-frames.mjs

@@ -1,4 +1,5 @@
 import { colourDistance } from '../lib/harness.mjs';
+import { openTab } from './lib/scaffold.mjs';
 
 /**
  * The Texture tab: cutting frames out of a sheet, and a sprite wearing one.
@@ -41,8 +42,8 @@ export async function frames(t) {
   await evaluate('__gm.state.select(null)');
   const texture = await json("(__gm.state.project.assets.find((a) => a.type === 'texture') ?? {}).id ?? ''");
   await evaluate(`__gm.state.select({ kind: 'asset', assetId: ${JSON.stringify(texture)} })`);
-  await clickText('Texture');
-  await sleep(600);
+  await openTab(t, 'texture');
+  await sleep(400);
   check('the Texture tab opens', (await json('__gm.tab()')) === 'texture');
   check(
     'and shows the selected sheet',