Optimize landing page conversion, performance, SEO, and accessibility

[cdcavell]

Summary

• restructure the landing page around an above-the-fold hero, clear calls to action, role/problem entry points, responsive learning-path cards, semantic process flows, and recent content
• fix the duplicated home title and align page, social, and structured-data descriptions
• defer DocFX search worker/index loading until the search field is used, remove the home page's duplicate TOC fetch path, and keep the internal DocFX build manifest out of the Pages artifact
• add a working skip link, decorative-icon handling, explicit logo dimensions/preload, focused styles, and generated-site regression checks

Acceptance evidence

• At 375 x 812, Get Started is fully visible at 445 px from the viewport top.
• The generated title is Governed Execution & Secure .NET Architecture Tutorials | ASI Backbone Learning.
• Browser verification shows data-search-index="deferred" before interaction and ready after a search returns results; the initial load does not request search-worker.min.js or index.json.
• The home page emits only docfx:navrel, so toc.json is fetched once rather than twice.
• Keyboard verification moves focus from Skip to content to main-content.

Lighthouse 12.8.2 mobile

Audit	Performance	Accessibility	SEO	Requests	Transfer
Published baseline	74	99	92	15	1,521 KB
Local change	69	100	92	10	627 KB

The local DocFX server does not provide GitHub Pages compression or cache headers, so its performance score is not directly comparable to the hosted baseline. The request trace confirms that the initial page no longer loads the 3.1 MB search index, search worker, es-* syntax/Mermaid chunk, or a second toc.json request.

Validation

• dotnet run --file tools/validate-docfx-template-baseline.cs
• dotnet tool run docfx docs/docfx.json --warningsAsErrors
• sitemap self-test, generation, and validation
• IndexNow self-test and dry run
• RSS feed self-test and generation
• X publisher self-test
• dotnet run --file tools/validate-doc-metadata.cs
• dotnet restore Samples.slnx --locked-mode
• dotnet build Samples.slnx --no-restore
• dotnet format Samples.slnx --verify-no-changes --no-restore --verbosity minimal
• dotnet test Samples.slnx --no-build (300 passed)

Closes #334