fix: correct block name in vendor messages template

Changed {% block page_scripts %} to {% block extra_scripts %} to match
the vendor base template. This was preventing messages.js from loading,
causing all the Alpine.js variable errors (dark, isSideMenuOpen, etc.)

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

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

app/templates/vendor/messages.html

@@ -286,6 +286,6 @@
 </div>
 {% endblock %}
 
-{% block page_scripts %}
+{% block extra_scripts %}
 <script src="{{ url_for('static', path='vendor/js/messages.js') }}"></script>
 {% endblock %}