Implement historical tracking using django-pghistory; add middleware for context capture and update model architecture

memory-bank/workflows/moderation.md

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+## Updated Moderation Workflow with django-pghistory
+
+### Submission Lifecycle
+1. **Change Proposal**  
+   - Creates `pending` pghistory event with metadata:  
+     ```python
+     pghistory.track(
+         pghistory.Snapshot('submission.pending'),
+         status='pending'
+     )
+     ```
+2. **Approval Process**  
+   - Merges event into main history:  
+     ```python
+     event.pgh_label = 'approved_change'
+     event.pgh_context['approver'] = request.user
+     ```
+3. **Rejection Handling**  
+   - Preserves event with rejection context:  
+     ```python
+     event.pgh_label = 'rejected_change'
+     event.pgh_context['reason'] = rejection_reason
+     ```
+
+### Moderation Admin Integration
+```python
+# moderation/admin.py
+@admin.register(pghistory.models.Event)
+class HistoryAdmin(admin.ModelAdmin):
+    list_display = ('pgh_label', 'pgh_created_at', 'content_object')
+    readonly_fields = ('pgh_data', 'pgh_context')