Redesign specification to use JSONLines with UUID-based directories

- Change from SQLite to JSONLines file-based storage
- UUID per task with dedicated directory structure
- Separate running/ and completed/ directories for lifecycle management
- Remove code examples, focus on specification only
- Add detailed file formats, locking mechanisms, and multiprocess coordination
- Include full implementation phases without migration considerations

Co-authored-by: notfolder <20558197+notfolder@users.noreply.github.com>

Author: Copilot