Add invite links with admin-configurable config creation limits.

Admins can create shareable links that allow redeeming a VPN config a set number of times (or unlimited).

Co-authored-by: Cursor <cursoragent@cursor.com>

templates/base.html

@@ -45,6 +45,7 @@
                 {% if current_user.role in ['admin', 'support'] %}
                 <a href="/" class="nav-link">{{ _('nav_servers') }}</a>
                 <a href="/users" class="nav-link">{{ _('nav_users') }}</a>
+                <a href="/invites" class="nav-link">{{ _('nav_invites') }}</a>
                 {% endif %}
                 {% if current_user.role == 'admin' %}
                 <a href="/settings" class="nav-link">{{ _('nav_settings') }}</a>