034: rewrite relative .md links to .html via jekyll-relative-links

Cross-doc links like [Coverage](coverage.md) were 404ing on the
deployed site because Jekyll left the .md extension as-is while pages
are served as .html. Add the jekyll-relative-links plugin (designed
exactly for this) to auto-rewrite all relative *.md links to their
*.html counterparts during build. No source-file edits needed — the
same links continue to work on GitHub and on the docs site.

Author: angelovstanton

docs/Gemfile

@@ -3,6 +3,7 @@ source "https://rubygems.org"
 gem "jekyll", "~> 4.3"
 gem "just-the-docs", "~> 0.10"
 gem "jekyll-seo-tag", "~> 2.8"
+gem "jekyll-relative-links", "~> 0.6"
 
 # Windows / JRuby support (no-op on Linux runners)
 platforms :mingw, :x64_mingw, :mswin, :jruby do

docs/_config.yml

@@ -53,6 +53,13 @@ back_to_top_text: "Back to top"
 # Plugins
 plugins:
   - jekyll-seo-tag
+  - jekyll-relative-links
+
+# jekyll-relative-links: rewrite relative *.md links to their built
+# *.html counterparts so cross-doc references work on the deployed site.
+relative_links:
+  enabled: true
+  collections: true
 
 # Default layout for every page (Just the Docs sidebar + header)
 defaults: