refactor(studio): remove unused types.ts file

- Remove stale Task-related type definitions
- These types were never imported or used in the codebase
- Part of Phase 1.6 code cleanup task

Agent-Logs-Url: https://github.com/objectstack-ai/framework/sessions/6c441201-fefb-4ec4-90de-2d3cd9f043db

Co-authored-by: hotlong <50353452+hotlong@users.noreply.github.com>

Author: Claude