Document the Footer/TrustRow lg: regression and the Playwright verification method

Both components were wrongly reclassified as plain sm: renames during
the 640px migration; they'd been on lg: for a genuine fixed-content-
width reason, not the fluid-floor bug the migration targets. Also
documents that a real headless-browser check (Playwright, installed
into a scratch dir) is available in this environment after all —
caught both regressions via scrollWidth vs. innerWidth measurements
against the live site.

README.md

@@ -1895,6 +1895,15 @@ moving both the fluid floor and the structural switch down together, from
 No browser/screenshot tool is available in this environment, so this
 migration is verified by typecheck/build/lint/`test:unit` only — actual
 visual confirmation at 640/768/1024/1440px is still owed by the user.
+**Update, same day:** a real headless-browser check turned out to be
+possible after all — `npx playwright install chromium` in a scratch
+directory, then a plain Node script driving `playwright`'s `chromium.launch()`
+against the *live* site at a specific viewport, reading
+`document.documentElement.scrollWidth` vs. `window.innerWidth` (a real
+horizontal overflow, not just "looks cramped") and `getBoundingClientRect()`
+on specific elements. This is a real, repeatable verification tool for
+future Tablet-layout work in this environment — see the two regressions
+below, both caught this way, not by guessing from a screenshot.
 
 Same session: **`Hero.tsx`'s heading** shortened from two sentences
 ("Verliere dich nicht im Mehr. Finde heraus, was wichtig ist.") to one
@@ -1905,6 +1914,28 @@ lengthened to match the other two cards' length (see the Payload repo's
 own README for the `fix-3x3-copy-length.ts` one-off that changed the
 live content).
 
+**Correction, 2026-07-29 (later the same day): `Footer.tsx`'s legal-links
+row and `TrustRow.tsx` were wrongly reclassified as plain `sm:` renames
+above.** Both had originally used `lg:flex-row` for a genuine
+fixed-content-width reason (logo + handle + 5 `whitespace-nowrap` legal
+links; multiple `whitespace-nowrap` title+description trust badges) — not
+the "grid arrives before the fluid floor" bug the `sm:` migration
+targets. Renaming them to `sm:` during the mechanical mass-rename pass
+caused a **real horizontal page overflow** in the 640-1023px band on
+every page that renders them (Footer: every page; TrustRow: shop, cart,
+checkout, order-confirmation, `/agb`, `/widerruf`, `/not-found`) —
+confirmed via the Playwright method above: `scrollWidth` exceeded the
+viewport by ~80-100px at 666-768px viewports. Both reverted to `lg:`,
+matching their original (correct) behavior; `TrustRow.tsx` also now
+centers its badges when stacked (`items-center` throughout, was
+`items-start` below `sm:`) per follow-up feedback. **Lesson: "this looks
+like the same md:→sm: pattern as everything else" isn't sufficient
+justification on its own — check whether a component was *already* on
+`lg:` for a real fixed-width-content reason (not just inherited from an
+earlier, unrelated Tablet fix) before reclassifying it as a mechanical
+rename.** See the `figma-to-nextjs` skill's Gotcha 21 for the fuller
+writeup.
+
 ## Tests
 
 `npm run test:unit` (Vitest, `node` environment, no jsdom/Next.js runtime