feat: basic admin interface

app/pages/auth/register.vue

@@ -12,9 +12,10 @@ if (session.value !== null) {
     await navigateTo(to ?? '/');
 }
 
-const config = useRuntimeConfig();
+// who may register is an instance setting, admins change it while it runs
+const { data: instance } = await useFetch('/api/instance', { key: 'instance' });
 
-if (config.public.disableSignup) {
+if (instance.value && instance.value.registration !== 'open') {
     await navigateTo(to ? `/auth/login?to=${to}` : '/auth/login');
 }
 
@@ -121,6 +122,10 @@ const submit = async () => {
                 passwordInputEl.value!.setCustomValidity(res.error.data.message!);
                 passwordInputEl.value!.reportValidity();
                 break;
+            case 'REGISTRATION_CLOSED':
+                // an admin closed registration while this page was open
+                alert('Registration is closed on this instance. Ask an admin for an account.');
+                break;
             default:
                 console.log(res.error);
                 alert('Something went wrong: ' + res.error.data.message);