feat: pass the Starlight gate on dense pages

Pages of cards under one or two headings drop the table of contents,
whose script watched every block of a 400-card page: 2 x 430 ms of
main thread on a throttled phone. Tables are measured once the page is
idle, skipping those in closed blocks, so a scrolling table is a tab
stop anywhere on the page. The 12 heaviest pages score 97 to 100 in
Lighthouse mobile, axe reports nothing on 16 pages in both themes, and
the search answers the ten gate queries.

website/tools/check_tools.mjs

@@ -71,6 +71,9 @@ console.log('glossary term:', await term.textContent(), '=', await term.getAttri
 // On a phone, a table whose rows end in a download is one block per row.
 await page.setViewportSize({ width: 390, height: 844 });
 await page.goto(`${base}which-pack/`, { waitUntil: 'networkidle' });
+// Tables are set up as they near the screen.
+await page.locator('table:has(a[href*="/releases/download/"])').first().scrollIntoViewIfNeeded();
+await page.waitForTimeout(300);
 const stacked = await page.locator('table[data-rb-stack]').count();
 const overflow = await page.evaluate(() => document.documentElement.scrollWidth > innerWidth + 1);
 console.log('stacked tables:', stacked, 'page wider than the phone:', overflow);