Add contact form with reCAPTCHA, saved to DB, viewable in admin

Adds a public /contact page (name/email/message, protected by the same
reCAPTCHA v3 setup used on registration) that persists submissions to
a new contact_message table, plus a Contact section in the admin panel
to read them. Linked from the site footer.

templates/layout/site.html.twig

@@ -67,6 +67,8 @@
 <footer class="site-footer py-4">
     <div class="container text-center small">
         <div class="mb-1">
+            <a href="{{ path('website_contact') }}" class="link-light">{{ 'footer.contact'|trans }}</a>
+            &middot;
             <a href="{{ path('website_help_wanted') }}" class="link-light">{{ 'footer.help_wanted'|trans }}</a>
             &middot;
             <a href="{{ path('website_terms') }}" class="link-light">{{ 'footer.terms'|trans }}</a>