fix(brain): correct stageDetails map generics for persistence

Co-authored-by: Venkat SF <venkatesh.sakamuri@stayflexi.com>

Author: cursoragent

backend/src/main/java/com/dbaagent/service/scheduler/BrainInitStageExecutor.java

@@ -729,7 +729,7 @@ private void recordStageDetails(ConnectionInitStatus status, InitStage stage, Ma
                 return;
             }
             ConnectionInitStatus fresh = current.get();
-            Map<String, Object> merged = fresh.getStageDetails() != null
+            Map<String, Map<String, Object>> merged = fresh.getStageDetails() != null
                 ? new HashMap<>(fresh.getStageDetails())
                 : new HashMap<>();
             merged.put(stage.name(), new HashMap<>(details));