chore(delegate-task): remove unused execute field from DelegateTaskArgs

The execute field with { task_id, task_dir } was defined but never referenced anywhere in the codebase. Removing dead code simplifies the type surface and prevents accidental future misuse.

Ultraworked with [Sisyphus](https://github.com/code-yeongyu/oh-my-openagent)

Co-authored-by: Sisyphus <clio-agent@sisyphuslabs.ai>

src/tools/delegate-task/types.ts

@@ -19,10 +19,6 @@ export interface DelegateTaskArgs {
   task_id?: string
   command?: string
   load_skills: string[]
-  execute?: {
-    task_id: string
-    task_dir?: string
-  }
 }
 
 export interface ToolContextWithMetadata {