Align ConfigManager with DataSync's per-file pipeline format (pipeline.*.json)
by reusing EtlPipelineConfig types directly, eliminating duplicate models and
simplifying the codebase. Removes ~3200 lines of obsolete code.
Tests cover:
- Loading from model
- Serializing to model
- Test pattern command (success and error cases)
- Mode switching and help text
- Summary display
- Change notification