Add GitHub source code link to homepage footer

Add open source attribution and GitHub link at bottom of homepage.
Styled subtly with centered text and tertiary color.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

kjvstudy_org/templates/index.html

@@ -489,4 +489,10 @@ document.addEventListener('keydown', function(e) {
 
     <p><span class="newthought">Chronology</span> — A <a href="/biblical-timeline">timeline of biblical events</a>, presenting in ordered sequence the principal occurrences recorded in Scripture, from the creation to the apostolic age.</p>
 </section>
+
+<div style="margin-top: 3rem; padding-top: 1rem; border-top: 1px solid var(--border-color); text-align: center;">
+    <p style="font-size: 0.85rem; color: var(--text-tertiary);">
+        This project is open source. <a href="https://github.com/kennethreitz/kjvstudy.org" target="_blank" rel="noopener" style="color: var(--text-tertiary); border-bottom: 1px dotted var(--border-color-dark);">View the source code on GitHub</a>.
+    </p>
+</div>
 {% endblock %}