fix: add heading IDs to HTML build so TOC anchor links work on GitHub Pages

marked was rendering headings without id attributes, breaking all same-page
anchor links in table of contents sections. Added a custom heading renderer
using GitHub's anchor algorithm (lowercase, strip punctuation, spaces to hyphens).

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: taylorarndt

html/ACCESSIBILITY_TESTING.html

@@ -58,17 +58,17 @@
     </div>
   </header>
   <main id="main-content" class="markdown-body">
-    <h1>HTML Documentation Build System</h1>
+    <h1 id="html-documentation-build-system">HTML Documentation Build System</h1>
 <p>This repository converts all Markdown files to accessible HTML. The HTML output is committed alongside the Markdown source so that both formats are always in sync.</p>
-<h2>Quick Start</h2>
-<h3>View HTML Documentation</h3>
+<h2 id="quick-start">Quick Start</h2>
+<h3 id="view-html-documentation">View HTML Documentation</h3>
 <p>All HTML files live in the <code>html/</code> directory:</p>
 <ul>
 <li>Open <code>html/index.html</code> in your browser for the homepage</li>
 <li>Browse the <code>html/docs/</code> folder for chapter and appendix pages</li>
 <li>All internal links between documents are preserved</li>
 </ul>
-<h3>Build Commands</h3>
+<h3 id="build-commands">Build Commands</h3>
 <pre><code class="hljs language-bash"><span class="hljs-comment"># Install dependencies (first time only)</span>
 npm install
 
@@ -80,7 +80,7 @@ <h3>Build Commands</h3>
 
 <span class="hljs-comment"># Clean generated files</span>
 npm run clean</code></pre>
-<h2>How It Works</h2>
+<h2 id="how-it-works">How It Works</h2>
 <p>The build is run <strong>locally</strong> before committing. There is no CI pipeline - you build the HTML yourself and commit both the <code>.md</code> source and the <code>html/</code> output in the same commit.</p>
 <p><strong>Typical workflow:</strong></p>
 <ol>
@@ -89,15 +89,15 @@ <h2>How It Works</h2>
 <li>Stage and commit everything: <code>git add -A &amp;&amp; git commit -m &quot;docs: update chapter 6 and rebuild HTML&quot;</code></li>
 <li>Push</li>
 </ol>
-<h3>What Gets Converted</h3>
+<h3 id="what-gets-converted">What Gets Converted</h3>
 <ul>
 <li><code>docs/*.md</code> → <code>html/docs/*.html</code></li>
 <li><code>learning-room/**/*.md</code> → <code>html/learning-room/**/*.html</code></li>
 <li><code>README.md</code> → <code>html/index.html</code></li>
 <li><code>CONTRIBUTING.md</code> → <code>html/CONTRIBUTING.html</code></li>
 <li>All other root-level <code>.md</code> files</li>
 </ul>
-<h3>HTML Features</h3>
+<h3 id="html-features">HTML Features</h3>
 <p><strong>Style and Layout:</strong></p>
 <ul>
 <li>GitHub-flavored Markdown styling (familiar appearance)</li>
@@ -120,17 +120,17 @@ <h3>HTML Features</h3>
 <li>Footer with return link</li>
 <li>Preserves all internal links between documents</li>
 </ul>
-<h2>Configuration Files</h2>
+<h2 id="configuration-files">Configuration Files</h2>
 <ul>
 <li><strong>Build script:</strong> <code>scripts/build-html.js</code> - Conversion logic</li>
 <li><strong>Dependencies:</strong> <code>package.json</code> - Node.js packages (marked, highlight.js, etc.)</li>
 </ul>
-<h2>Customization</h2>
-<h3>Modify Styling</h3>
+<h2 id="customization">Customization</h2>
+<h3 id="modify-styling">Modify Styling</h3>
 <p>Edit <code>scripts/build-html.js</code> and look for the <code>customCss</code> constant to add custom styles.</p>
-<h3>Change HTML Template</h3>
+<h3 id="change-html-template">Change HTML Template</h3>
 <p>Edit the <code>htmlTemplate</code> function in <code>scripts/build-html.js</code> to modify the page structure.</p>
-<h3>Update Dependencies</h3>
+<h3 id="update-dependencies">Update Dependencies</h3>
 <pre><code class="hljs language-bash"><span class="hljs-comment"># Check for updates</span>
 npm outdated
 
@@ -140,8 +140,8 @@ <h3>Update Dependencies</h3>
 <span class="hljs-comment"># Commit package.json changes</span>
 git add package.json
 git commit -m <span class="hljs-string">&quot;chore: update HTML build dependencies&quot;</span></code></pre>
-<h2>Troubleshooting</h2>
-<h3>Local Build Errors</h3>
+<h2 id="troubleshooting">Troubleshooting</h2>
+<h3 id="local-build-errors">Local Build Errors</h3>
 <p><strong>&quot;Cannot find module &#39;marked&#39;&quot;</strong>
 → Run <code>npm install</code> first</p>
 <p><strong>&quot;Permission denied&quot; errors</strong>
@@ -150,16 +150,16 @@ <h3>Local Build Errors</h3>
 → Clear browser cache and reload</p>
 <p><strong>Watch mode not detecting changes</strong>
 → Ensure you&#39;re saving files (Ctrl+S in VS Code)</p>
-<h3>HTML Files Not Appearing in Git</h3>
+<h3 id="html-files-not-appearing-in-git">HTML Files Not Appearing in Git</h3>
 <p>Check <code>.gitignore</code> to ensure <code>html/</code> is NOT listed there. The <code>html/</code> directory must be tracked by Git so the built output is always available in the repository.</p>
-<h2>For Contributors</h2>
+<h2 id="for-contributors">For Contributors</h2>
 <p>When submitting pull requests:</p>
 <ul>
 <li><strong>Edit the Markdown files</strong>, then run <code>npm run build:html</code></li>
 <li><strong>Include both</strong> the <code>.md</code> changes and the updated <code>html/</code> files in your commit</li>
 <li>If you forget to rebuild, a reviewer will ask you to run the build before merging</li>
 </ul>
-<h2>Additional Resources</h2>
+<h2 id="additional-resources">Additional Resources</h2>
 <ul>
 <li><a href="https://marked.js.org/">marked documentation</a> - Markdown parser</li>
 <li><a href="https://highlightjs.org/">highlight.js documentation</a> - Syntax highlighting</li>