Add bounded batch enable and disable actions for Studio users

### Problem\n\nStudio administrators can only enable or disable local accounts one at a time. Operational changes involving many accounts require repeated manual actions and provide no consolidated view of partial failures.\n\n### Proposed solution\n\nAdd page-level multi-select and a batch status drawer that:\n\n- excludes the current login identity;\n- skips users already in the desired state;\n- uses the existing per-user API with a concurrency limit of four;\n- preserves per-user successes and failures;\n- supports retrying only failed items;\n- refreshes and clears selection after completion.\n\nSuccessful updates are not rolled back when another account fails, and the confirmation copy states that disabling accounts invalidates their sessions.

Start at the Studio user-management entry point and trace the existing per-user enable/disable API. Verify how selection, account state, and confirmation UI are handled, then check that bounded batch execution preserves individual results, retries only failures, refreshes the list, and clears selection after completion.

Written by the indexing model from the issue text.