refactor(expand): Align expand-task with unified AI service

Refactored the `expandTask` feature (`scripts/modules/task-manager/expand-task.js`) and related components (`commands.js`, `mcp-server/src/tools/expand-task.js`, `mcp-server/src/core/direct-functions/expand-task.js`) to integrate with the unified AI service layer (`ai-services-unified.js`) and configuration management (`config-manager.js`).

The refactor involved:

- Removing direct AI client calls and configuration fetching from `expand-task.js`.

- Attempting to use `generateObjectService` for structured subtask generation. This failed due to provider-specific errors (Perplexity internal errors, Anthropic schema translation issues).

- Reverting the core AI interaction to use `generateTextService`, asking the LLM to format its response as JSON containing a "subtasks" array.

- Re-implementing manual JSON parsing and Zod validation (`parseSubtasksFromText`) to handle the text response reliably.

- Updating prompt generation functions (`generateMainSystemPrompt`, `generateMainUserPrompt`, `generateResearchUserPrompt`) to request the correct JSON object structure within the text response.

- Ensuring the `expandTaskDirect` function handles pre-checks (force flag, task status) and correctly passes the `session` context and logger wrapper to the core `expandTask` function.

- Correcting duplicate imports in `commands.js`.

- Validating the refactored feature works correctly via both CLI (`task-master expand --id <id>`) and MCP (`expand_task` tool) for main and research roles.

This aligns the task expansion feature with the new architecture while using the more robust text generation approach due to current limitations with structured output services. Closes subtask 61.37.

mcp-server/src/tools/expand-task.js

@@ -9,9 +9,8 @@ import {
 	createErrorResponse,
 	getProjectRootFromSession
 } from './utils.js';
-import { expandTaskDirect } from '../core/task-master-core.js';
+import { expandTaskDirect } from '../core/direct-functions/expand-task.js';
 import { findTasksJsonPath } from '../core/utils/path-utils.js';
-import fs from 'fs';
 import path from 'path';
 
 /**
@@ -28,16 +27,26 @@ export function registerExpandTaskTool(server) {
 			research: z
 				.boolean()
 				.optional()
-				.describe('Use Perplexity AI for research-backed generation'),
+				.default(false)
+				.describe('Use research role for generation'),
 			prompt: z
 				.string()
 				.optional()
 				.describe('Additional context for subtask generation'),
-			file: z.string().optional().describe('Absolute path to the tasks file'),
+			file: z
+				.string()
+				.optional()
+				.describe(
+					'Path to the tasks file relative to project root (e.g., tasks/tasks.json)'
+				),
 			projectRoot: z
 				.string()
 				.describe('The directory of the project. Must be an absolute path.'),
-			force: z.boolean().optional().describe('Force the expansion')
+			force: z
+				.boolean()
+				.optional()
+				.default(false)
+				.describe('Force expansion even if subtasks exist')
 		}),
 		execute: async (args, { log, session }) => {
 			try {