security: add |esc_url to all template URLs, register escape Twig filters (v1.1.3)

5th OWASP Top-10 pass: added |esc_url filter to all unescaped URL outputs
across 8 Twig template partials (headers, footers, search, comments).
Registered esc_html, esc_attr, esc_url as Twig filters with is_safe option.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

views/partials/footer.html.twig

@@ -11,7 +11,7 @@
                         <ul class="list-unstyled">
                         {% for item in footer_menu %}
                             <li>
-                                <a href="{{ item.url }}" class="text-body-secondary text-decoration-none">
+                                <a href="{{ item.url|esc_url }}" class="text-body-secondary text-decoration-none">
                                     {{ item.title }}
                                 </a>
                             </li>