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.

translations/messages.en.yaml

@@ -9,6 +9,7 @@ nav.register: Register
 nav.logout: Logout
 link.enter_game: Enter the Game Area
 link.back_to_website: Back to Website
+footer.contact: Contact
 footer.help_wanted: Looking for Help
 footer.terms: Terms and Conditions