feat: add admin user management and disable public registration

apps/api/test/privacy.test.ts

@@ -1,3 +1,4 @@
+import { provisionTestUser } from './user-fixture';
 import { fixtureFetch } from './backup-fixture';
 import 'dotenv/config';
 import { test } from 'node:test';
@@ -31,7 +32,8 @@ test('privacy, minute history, backup-gated clear and idle sessions remain user
     const username = 'wp_privacy_' + randomUUID(),
       password = randomBytes(18).toString('hex');
     names.push(username);
-    const r = await call('/auth/register', 'POST', { username, password });
+    await provisionTestUser({ username, password });
+    const r = await call('/auth/login', 'POST', { username, password });
     assert.equal(r.status, 201);
     const u = await db.user.findUniqueOrThrow({ where: { username } });
     return { ...r, username, password, id: u.id };