[WM-IMP-7] No remediation-to-POA&M structural link — remediation tasks not connected to POA&M items

## WM-IMP-7 — Remediation Tasks Not Structurally Linked to POA&M Items

**Category:** Improvement | **Priority:** Medium

### Observation
Remediation tasks exist independently from POA&M items. There is no structural link connecting a remediation task to the POA&M item it is meant to close.

### Recommendation
Add a FK from remediation tasks to POA&M items. POA&M item status should auto-update based on linked remediation task completion.

### Acceptance Criteria
- [ ] Remediation task record includes optional FK to POA&M item
- [ ] POA&M item displays linked remediation tasks and their status
- [ ] Completing a remediation task can auto-transition the linked POA&M item to Closed state (with review gate)
- [ ] POA&M export includes remediation task references