ApiDoc: add a layout switch and optionally enable side bar

[cmil]

Scalar's classic layout never updates the URL hash for individual operations, so it is not obvious to readers how to link to a specific endpoint. The modern layout does. This PR lets readers switch between the two layouts, and hides Scalar's promotional sidebar buttons.

Layout switch

<ApiDoc
  url="/api/v1/openapi.yaml"
  layoutSwitch={{ modern: { showSidebar: true } }}
  configuration={{ layout: 'modern' }}
/>

• layoutSwitch (true or an options object) shows a Modern / Classic switch in the top right corner.
  • The choice is saved in localStorage under dracor.apiDocLayout by default. storageKey changes the key.
  • configuration.layout sets the layout used until the reader picks one.
  • Switching layouts rebuilds the Scalar view from scratch rather than changing the running instance.
• layoutSwitch.modern / layoutSwitch.classic apply extra configuration only while that layout is active. Each is merged on top of configuration, and its customCss is added rather than replacing the base CSS.
  • The main use is a sidebar in the modern layout only. On wide screens the modern layout has no search button outside the sidebar.
• Narrow screens: below Scalar's lg breakpoint, the modern layout shows a sticky header. To keep it clear of the switch:
  • its search button is capped at the classic layout's width (max-w-64);
  • the sidebar breadcrumb is truncated;
  • the header gets some space below its bottom border.

The sidebar is still off by default (showSidebar: false).

Scalar promo buttons

• New defaults: mcp: { disabled: true } and hideClientButton: true. These remove the "Generate MCP" button (shown on localhost) and the "Open API Client" button (shown elsewhere) from the sidebar footer. The per-endpoint "Test Request" buttons have their own option and are not affected.
• New hidePoweredBy prop: hides the "Powered by Scalar" link with CSS, since Scalar has no option for it. It is off by default.

Notes

• Depends on Scalar internals: the narrow-header and powered-by rules use selectors from Scalar's DOM (.t-doc__header, .darklight-reference). They may need updating when Scalar changes its markup.
• Version bump not included: package.json is still on 1.9.0. Since this only adds props, it can go out as 1.10.0.

Testing

• Unit tests cover the switch (default, switching, saving, restoring, bad saved value, custom key), per-layout configuration, the sidebar default, the hidden buttons, and the hidePoweredBy CSS. All 16 ApiDoc tests pass, as do pnpm lint and pnpm build.
• New LayoutSwitch Storybook story.
• Tested in dracor-frontend (/doc/api) with a packed tarball.

🤖 Generated with Claude Code

[codecov]

Codecov Report

❌ Patch coverage is 93.33333% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 95.41%. Comparing base (952dc90) to head (dc41140).

Files with missing lines	Patch %	Lines
src/components/ApiDoc/ApiDoc.tsx	93.33%	1 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #98      +/-   ##
==========================================
- Coverage   95.62%   95.41%   -0.21%     
==========================================
  Files          34       34              
  Lines         320      349      +29     
  Branches      109      122      +13     
==========================================
+ Hits          306      333      +27     
- Misses          3        4       +1     
- Partials       11       12       +1     

☔ View full report in Codecov by Harness.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.
• 📦 JS Bundle Analysis: Save yourself from yourself by tracking and limiting bundle sizes in JS merges.