fix(backend): merge settings instead of replacing on partial updates

When updating graph settings (e.g., toggling HITL safe mode), the backend
was replacing ALL settings with defaults instead of merging the update.

This caused toggling human_in_the_loop_safe_mode to also reset
sensitive_action_safe_mode to its default value (false).

Fix: Fetch existing settings, merge with new values using model_dump(exclude_unset=True),
then save the merged result. This preserves unchanged settings.

autogpt_platform/backend/backend/api/features/library/db.py

@@ -583,7 +583,13 @@ async def update_library_agent(
             )
         update_fields["isDeleted"] = is_deleted
     if settings is not None:
-        update_fields["settings"] = SafeJson(settings.model_dump())
+        existing_agent = await get_library_agent(id=library_agent_id, user_id=user_id)
+        current_settings_dict = (
+            existing_agent.settings.model_dump() if existing_agent.settings else {}
+        )
+        new_settings = settings.model_dump(exclude_unset=True)
+        merged_settings = {**current_settings_dict, **new_settings}
+        update_fields["settings"] = SafeJson(merged_settings)
 
     try:
         # If graph_version is provided, update to that specific version