refactor: rename sisyphus_task to delegate_task

- Rename directories: sisyphus-task → delegate-task
- Rename types: SisyphusTaskArgs → DelegateTaskArgs, etc.
- Rename functions: createSisyphusTask → createDelegateTask
- Rename constants: SISYPHUS_TASK_* → DELEGATE_TASK_*
- Update tool name: sisyphus_task → delegate_task
- Update all prompts, docs, and tests

src/tools/delegate-task/index.ts

@@ -0,0 +1,3 @@
+export { createDelegateTask, type DelegateTaskToolOptions } from "./tools"
+export type * from "./types"
+export * from "./constants"