- Add permissions.go with permission definitions and checks
- Define permissions for all 21 S3 Tables operations
- Add permission checking helper functions
- Add getPrincipalFromRequest to extract caller identity
- Implement access control in CreateTableBucket, GetTableBucket, DeleteTableBucket
- Return 403 Forbidden for unauthorized operations
- Only bucket owner can perform operations (extensible for future policies)
- Add AuthError type for authorization failures
