Fix workshop page gutters and interactive target sizing

[Copilot]

The rendered workshop page used a 16px mobile gutter because Primer’s .px-3 utility overrode the intended .markdown-body padding. Several rendered links and <summary> controls also measured below the 44×44px interaction target requirement.

• Responsive gutters

  • Ensures .markdown-body keeps at least a 20px inline gutter below 480px.
  • Preserves existing wider breakpoint gutters while overriding Primer utility padding.

• Interactive targets

  • Adds 44px minimum target sizing for visible body links, nested summaries, workshop nav buttons, side-menu links, and the footer link.
  • Uses inline-flex alignment so text links keep their visual style while gaining accessible hit area.

• Regression coverage

  • Extends docs build tests to assert the emitted gutter and target-size CSS.

.markdown-body {
  padding-inline: 20px !important;
}

.markdown-body a:not(.anchor):not(.workshop-nav-btn),
.workshop-navigation a:not(.anchor):not(.workshop-nav-btn) {
  display: inline-flex;
  align-items: center;
  min-width: 44px;
  min-height: 44px;
}

• Fixes [workshop-playwright-qa] __root__: 2 QA findings — brand, accessibility #2486