feat: add task_update and task_comment tools (#33)

Closes #26

This PR adds two new DevClaw tools for better task lifecycle management:

- task_update: Change issue state programmatically without full pickup/complete flow
- task_comment: Add review comments or notes to issues with optional role attribution

lib/task-managers/task-manager.ts

@@ -75,6 +75,9 @@ export interface TaskManager {
   /** Check if any merged MR/PR exists for a specific issue. */
   hasMergedMR(issueId: number): Promise<boolean>;
 
+  /** Add a comment to an issue. */
+  addComment(issueId: number, body: string): Promise<void>;
+
   /** Verify the task manager is working (CLI available, auth valid, repo accessible). */
   healthCheck(): Promise<boolean>;
 }