Fix focus group create: 500 on update + 400 on autosave

- FocusGroup.update: use matched_count > 0 instead of modified_count > 0
  so updates succeed even when data is unchanged (was returning 500)
- useFocusGroupAutoSave: skip save if name is empty (not all-fields-empty)
  preventing 400 Bad Request when autosave fires before name is filled

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

backend/app/models/focus_group.py

@@ -149,8 +149,8 @@ class FocusGroup:
                     'updated_at': filtered_data["updated_at"].isoformat()
                 })
 
-        return result.modified_count > 0
-    
+        return result.matched_count > 0
+
     @staticmethod
     def _cleanup_focus_group_assets(focus_group_id, uploaded_assets):
         """Clean up all creative asset files for a focus group."""

src/hooks/useFocusGroupAutoSave.ts

@@ -99,8 +99,8 @@ export function useFocusGroupAutoSave({
         return; // No changes
       }
 
-      if (!currentData.name && !currentData.description && !currentData.topic) {
-        return; // Don't save empty form
+      if (!currentData.name) {
+        return; // Don't save without name (required by backend)
       }
 
       isSavingRef.current = true;