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

memory-bank/decisions/pghistory-integration.md

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+## Decision: Universal Model History via django-pghistory
+
+### Pattern Implementation
+- **Tracking Method**: `pghistory.Snapshot()` applied to all concrete models
+- **Inheritance Strategy**: Base model class with history tracking
+- **Context Capture**:
+  ```python
+  # core/models.py
+  import pghistory
+  
+  class HistoricalModel(models.Model):
+      class Meta:
+          abstract = True
+
+      @pghistory.track(pghistory.Snapshot())
+      def save(self, *args, **kwargs):
+          return super().save(*args, **kwargs)
+  ```
+
+### Integration Scope
+1. **Model Layer**:
+   - All concrete models inherit from `HistoricalModel`
+   - Automatic event labeling:
+     ```python
+     @pghistory.track(
+         pghistory.Snapshot('model.create'),
+         pghistory.AfterInsert('model.update'),
+         pghistory.BeforeDelete('model.delete')
+     )
+     ```
+
+2. **Context Middleware**:
+   ```python
+   # core/middleware.py
+   pghistory.context(lambda request: {
+       'user': str(request.user) if request.user.is_authenticated else None,
+       'ip': request.META.get('REMOTE_ADDR'),
+       'user_agent': request.META.get('HTTP_USER_AGENT'),
+       'session_key': request.session.session_key
+   })
+   ```
+
+3. **Admin Integration**:
+   - Custom history view for Django Admin
+   - Version comparison interface