refactor: remove legacy file-based storage code_task_v1.py

Removes the deprecated file-based task storage system as it has been 
replaced by the v2 Supabase-based system. This includes:
- Legacy in-memory task storage
- File persistence to tasks_backup.json  
- Deprecated run_ai_code_task() function
- Legacy Docker container execution code

Co-authored-by: Elwynn Chen <ObservedObserver@users.noreply.github.com>

Author: claude[bot]