feat: Enhance ID mapping service robustness, add defensive guards, and expand migration engine and API testing.

backend/src/core/mapping_service.py

@@ -101,11 +101,13 @@ class IdMappingService:
                         
                         for res in resources:
                             res_uuid = res.get("uuid")
-                            res_id = str(res.get("id")) # Store as string
+                            raw_id = res.get("id")
                             res_name = res.get(name_field)
 
-                            if not res_uuid or not res_id:
+                            if not res_uuid or raw_id is None:
                                 continue
+                            
+                            res_id = str(raw_id) # Store as string
 
                             # Upsert Logic
                             mapping = self.db.query(ResourceMapping).filter_by(