feat(mcp): Implement update-subtask MCP command for appending information to subtasks

mcp-server/src/core/task-master-core.js

@@ -10,6 +10,7 @@ import { getCacheStatsDirect } from './direct-functions/cache-stats.js';
 import { parsePRDDirect } from './direct-functions/parse-prd.js';
 import { updateTasksDirect } from './direct-functions/update-tasks.js';
 import { updateTaskByIdDirect } from './direct-functions/update-task-by-id.js';
+import { updateSubtaskByIdDirect } from './direct-functions/update-subtask-by-id.js';
 
 // Re-export utility functions
 export { findTasksJsonPath } from './utils/path-utils.js';
@@ -21,6 +22,7 @@ export {
   parsePRDDirect,
   updateTasksDirect,
   updateTaskByIdDirect,
+  updateSubtaskByIdDirect,
 };
 
 /**
@@ -33,5 +35,6 @@ export const directFunctions = {
   parsePRD: parsePRDDirect,
   update: updateTasksDirect,
   updateTask: updateTaskByIdDirect,
+  updateSubtask: updateSubtaskByIdDirect,
   // Add more functions as we implement them
 };