refactor: consolidate and simplify pipeline scripts

- Merge 8 scripts into 2 (convert.py, register.py)
- Normalize CONFIGS structure (groups always list, direct crs_groups)
- Use pystac native patterns (Item.clone, simplified workflow)
- Simplify registration: 6 HTTP calls → 2 (fetch+upsert)
- Add emoji logging for better UX
- Net reduction: -198 lines (-30%)

Author: wietzesuijker