fix: add rollback on rename failure and update PR description

- Roll back user migration if updateRoleByName returns null during a
  rename (race: role deleted between existence check and update)
- Add test verifying rollback calls updateUsersByRole in reverse
- Update PR #12400 description to reflect current test counts (56
  handler tests, 40 data-layer tests) and safety features

packages/api/src/admin/roles.ts

@@ -163,6 +163,9 @@ export function createAdminRolesHandlers(deps: AdminRolesDeps) {
 
       const role = await updateRoleByName(name, updates);
       if (!role) {
+        if (isRename) {
+          await updateUsersByRole(trimmedName, name);
+        }
         return res.status(404).json({ error: 'Role not found' });
       }