feat(seo): Google Search Console audit fixes, docs root elevation and SEO hygiene

[humanbydefinition]

Summary

This PR addresses crawl, indexing, canonical, and structured data issues discovered during a Google Search Console (GSC) audit of sc-domain:code.textmode.art, while streamlining documentation routing and site configuration.

Key Changes

1. Elevated Introduction to Documentation Root

• Moved docs/introduction.md to docs/index.md: Resolves the 404 error reported by Google Search Console on https://code.textmode.art/docs/ and https://code.textmode.art/docs.
• Navigation and Sidebar:
  • Updated nav.mts to point Documentation directly to /docs/.
  • Updated sidebar.mts so both the Start group header and the Introduction item link to /docs/.
  • Updated home hero Get started link and contributing guides to point to /docs/.

2. Canonical URL Normalization

• Refactored transformHead in head.mts:
  • Directory index pages (/, /docs/, /api/, /docs/contributing/) now receive trailing-slash canonical URLs matching GitHub Pages static server behavior.
  • Leaf pages (/gallery, /api/...) receive clean non-trailing-slash canonical URLs.
  • Eliminates GSC "Page with redirect" and "Alternate page with proper canonical tag" warnings.

3. Structured Data and Schema.org Enhancements

• Breadcrumb Validation: Fixed dynamic breadcrumb generation so all intermediate and leaf items resolve to valid 200 OK pages, eliminating 404 intermediate breadcrumbs on deep API reference pages.
• API Reference Schema: Injected structured TechArticle schema across all API reference pages.
• WebSite Schema: Removed nonexistent /search?q= SearchAction from root schema.

4. Blog Decommissioning and Crawl Blocking

• Excluded blog/** from VitePress builds and sitemap in config.mts.
• Removed vitepress-plugin-blog theme wrapper and configuration.
• Added Disallow: /blog/ and Disallow: /blog to public/robots.txt to prevent search bots from crawling deprecated blog paths.

5. Sitemap and Source Cleanup

• Added root repository markdown files (README.md, LICENSE.md, CONTRIBUTING.md, CODE_OF_CONDUCT.md, SECURITY.md, CONTRIBUTORS_AUTOMATION.md, and .vitepress/data/TESTIMONIALS_README.md) to srcExclude in config.mts.
• Resulting sitemap is reduced to 805 valid documentation and API reference URLs with zero orphans.

Verification

• Contributor validation test suite passes (node --test scripts/contributors.test.mjs).
• API examples scanner test suite passes (node --test scripts/api-examples.test.mjs).
• Full static build passes with 0 errors (vitepress build).
• Verified canonical tags on built HTML outputs (index.html, docs/index.html, api/index.html, gallery.html).
• Verified sitemap.xml contains 0 blog URLs, 0 orphan root markdown files, and includes /docs/.