M6: Admin Approval Workflow Complete

Deliverables:
- Approve post endpoint
- Schedule publish endpoint
- Delete post (Admin)
- Reapproval if updated

Completion Criteria:
- Post moves Draft -> Pending -> Approved -> Published correctly
- Admin can schedule a publish
- Deleted posts disappear from search
- Worker index updates correctly

Dependencies:
- Milestone 5 (worker events)
- Milestone 3 (post model)

No due date
50% Completed