Implement VaultProvider with Transit engine:
- AppRole, Kubernetes, and Token authentication
- Encrypt/Decrypt via /transit/encrypt and /transit/decrypt
- Key lifecycle via /transit/keys API
- Health check via /sys/health
Implement AWSProvider with SDK v2:
- Per-region key naming with alias prefix
- Encrypt/Decrypt via KMS SDK
- Key lifecycle (CreateKey, Disable, ScheduleDeletion, Enable)
- AWS endpoint support for LocalStack testing
