fix(mcp): convert silently swallowed OK string errors into explicit JSON-RPC errors for task transitions and bulk entity operations

server/src/handlers/tasks.rs

@@ -257,7 +257,7 @@ impl McpTool for UpdateTaskStatusHandler {
         });
 
         if blocked {
-            Ok(format!(
+            Err(format!(
                 "Error: Cannot transition task. {}",
                 blocker_details
             ))