- Move Server/Domain/DNSRecord/Bucket/StorageInstance/CDNInstance/Order/Error structs to internal/model/
- Provider interfaces now reference model.* types
- Rainyun provider implementations import model package for data types
- CLI commands updated to use model.DNSRecord directly
Separates pure data structures from service contract interfaces,
following hexagonal architecture: models (entities) live independently
from ports (provider interfaces) and adapters (rainyun/* implementations).
