fix: constrain workshop-navigation-next to 100% width on mobile

[Copilot]

On 375px viewports, div.workshop-navigation-next computed to ~430px wide (intrinsic button sizes), overflowing the markdown-body container (~360px) and producing a horizontal scrollbar.

Change

Added width: 100% to .workshop-navigation-next inside the existing @media (max-width: 543px) block in scripts/build-docs.js:

@media (max-width: 543px) {
  .workshop-navigation {
    flex-wrap: wrap;
    gap: 8px;
  }
  .workshop-navigation-next {
    align-items: stretch;
    width: 100%;   /* ← added */
  }
  /* … */
}

The base style sets flex: 0 0 auto on .workshop-navigation-next, preventing flex shrinking. width: 100% overrides that on mobile, clamping the element to the available container width. Combined with the existing flex-wrap: wrap on the parent and align-items: stretch on the element, buttons stack full-width cleanly on small screens.

• Fixes [workshop-playwright-qa] 07-your-first-workflow: 1 QA finding(s) — readability #1880