Fix: Article author update in Avo admin

- Add custom update_model_record method to handle author changes
- Properly manage polymorphic authorship association
- Destroy existing authorship before creating new one
- Handle removal of author (blank selection)

This ensures author changes are properly saved when editing articles in Avo.

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

Author: Shpigford

app/avo/resources/article.rb

@@ -23,4 +23,23 @@ def fields
       end
     end
   end
+
+  def update_model_record(model, params, **args)
+    author_id = params.delete(:author_id)
+
+    super(model, params, **args)
+
+    if author_id.present?
+      # Remove existing authorship if present
+      model.authorship&.destroy
+
+      # Create new authorship with the selected author
+      model.create_authorship(author_id: author_id, role: "primary")
+    elsif author_id == ""
+      # If author_id is blank, remove the authorship
+      model.authorship&.destroy
+    end
+
+    model
+  end
 end