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/config/schema.ts

@@ -84,7 +84,7 @@ export const HookNameSchema = z.enum([
   "claude-code-hooks",
   "auto-slash-command",
   "edit-error-recovery",
-  "sisyphus-task-retry",
+  "delegate-task-retry",
   "prometheus-md-only",
   "start-work",
   "sisyphus-orchestrator",