Add source_site_id to ActiveSite model and implement unique constraint. Update serializers and views for site registration and claiming. Enhance tests for site registration and claiming functionality.

components/UserManagementPage.tsx

@@ -87,7 +87,7 @@ const UserManagementPage: React.FC = () => {
           password,
         });
         setNotice(
-          `Akun "${userName.trim()}" dibuat. Bagikan password sementara secara aman (di luar sistem).`
+          `Akun "${userName.trim()}" dibuat. Jangan lupa ganti password setelah login pertama kali.`
         );
         setUserLogin('');
         setUserName('');
@@ -133,7 +133,7 @@ const UserManagementPage: React.FC = () => {
       setBusyId(id);
       try {
         await api.users.setPassword(id, resetPassword);
-        setNotice('Password direset. Bagikan password baru secara aman (di luar sistem).');
+        setNotice('Password direset. Bagikan password baru secara aman.');
         setResetId(null);
         setResetPassword('');
         await reload();