- Renamed folderDict to keyDict for clarity
- Updated internal storage to use serie.key instead of serie.folder
- Optimized contains() from O(n) to O(1) with direct key lookup
- Added get_by_key() as primary lookup method
- Added get_by_folder() for backward compatibility
- Enhanced docstrings to clarify key vs folder usage
- Created comprehensive test suite (12 tests, all passing)
- Verified no breaking changes (16 SeriesApp tests pass)
This establishes key as the single source of truth for series
identification while maintaining folder as metadata for filesystem
operations only.
