LOOPIN-019B — Implement admin moderation review API

[shaig-mahmudov]

• Type: Backend
• Priority: Medium
• Branch: feature/LOOPIN-019B-admin-moderation-api
• Description: Build endpoints allowing admins to approve or reject content marked as pending review.
• Acceptance Criteria:
  • Only users with ADMIN role can access these endpoints.
  • Action updates visibility status of content.