fix(portal): add Super User grant/revoke toggle to Staff page (GRO-206)

- Add isSuperUser boolean to Staff interface in types
- Fetch current user via /api/staff/me to determine if super user
- Show "Super User" column and Grant/Revoke buttons only for super users
- Disable revoke button when target is the last active super user
- Show API error messages when last-super-user guardrail triggers
- Prevent self-revocation (no Grant/Revoke button on own row)

Co-Authored-By: Paperclip <noreply@paperclip.ing>

packages/types/src/index.ts

@@ -72,6 +72,7 @@ export interface Staff {
   name: string;
   email: string;
   role: "groomer" | "receptionist" | "manager";
+  isSuperUser: boolean;
   active: boolean;
   createdAt: string;
   updatedAt: string;