feat: disable public registration in Forgejo docker configuration

forgejo/docker-compose.yml

@@ -19,6 +19,9 @@ services:
       
       # Disable installer screen since we configure via environment/app.ini
       - FORGEJO__security__INSTALL_LOCK=true
+      
+      # Disable public registration (prevent outside signups)
+      - FORGEJO__service__DISABLE_REGISTRATION=true
     ports:
       # Expose Forgejo HTTP port publicly
       - "3000:3000"