Horizontal overflow at three viewports, with the mask lifted

Add a horizontal-overflow sweep to the browser harness that runs at every breakpoint, sees through the global clip, and does not blame elements that are legitimately clipped.

**The probe** — a single exported function serialized into the page:

```js
export const OVERFLOW_CULPRITS = () => {
  const de = document.documentElement;
  const prev = document.body.style.overflowX;   // save
  document.body.style.overflowX = "visible";     // lift the mask
  void de.scrollWidth;                           // force reflow before measuring
  const vw = de.clientWidth;
  const overflow = de.scrollWidth - vw;
  const culprits = [];
  if (overflow > 1) {
    for (const el of document.querySelectorAll("body *")) {
      const r = el.getBoundingClientRect();
      if (!r.width || !r.height) continue;              // invisible
      if (r.right <= vw + 1 && r.left >= -1) continue;  // inside the viewport
      let clipped = false;
      for (let p = el.parentElement; p; p = p.parentElement) {
        if (/hidden|clip|auto|scroll/.test(getComputedStyle(p).overflowX)) { clipped = true; break; }
      }
      if (clipped) continue;   // a carousel doing its job, not the page being too wide
      culprits.push({
        tag: el.tagName.toLowerCase(),
        cls: typeof el.className === "string" ? el.className.slice(0, 70) : "",
        right: Math.round(r.right),
        width: Math.round(r.width),
      });
    }
  }
  document.body.style.overflowX = prev;  // restore — the page must be as you found it
  return { overflow, culprits: culprits.slice(0, 5) };
};
```

Four things in there are not optional and each one is a bug you would otherwise ship:
- **Lifting `overflow-x` on body**, or the global clip masks every offender and the audit is decorative.
- **`void de.scrollWidth`** to force a reflow after the style change, or you measure the pre-clip layout.
- **The clipped-ancestor walk**, or the check cries wolf on every marquee, carousel and ticker, which is how checks get deleted.
- **The restore**, because later checks run on the same page and must see the app's real styles. Assert the restoration in the probe's self-test — a probe that mutates the page and forgets to undo it poisons every measurement after it.

**Sweep the viewports.** Default `[1440×900, 768×1024, 390×844]`, and **read the project's own breakpoints** out of the Tailwind config or the stylesheet's media queries and add one viewport just inside each. After `setViewport`, wait ~600ms before measuring: media queries, ResizeObservers and any JS-driven layout need a frame or several. Run the sweep on every route, not just the homepage — the marketing hero is rarely the thing that overflows.

**Fail per viewport**, naming the offenders:

```
FAIL  overflow  /features @ 390px
      document is 214px wider than the viewport
      div.grid.gap-8 — right edge 604px, width 604px
      img.hero — right edge 512px, width 512px
```

The overflow amount alone is not actionable at 390px, where a dozen things could be responsible. Sort culprits by `right` descending so the worst offender is the first line.

**Do not** add the check by asserting `document.body.scrollWidth === window.innerWidth` and calling it done — that is the same number without the culprit list, and it will also read clean through the clip. **Do not** try to fix overflow by adding more `overflow-x: hidden`; if the check fires and someone's remedy is another clip, the check has made the codebase worse. Say this in the failure text.

**Hand back:** the probe, the sweep, and a run against this project at all viewports with the real numbers.