Introduce ErrMixedOrganizationBatch, ErrMixedEntityTypeBatch,
ErrEmptyResourceBatch, and ErrBatchAuthorizationUnsupportedResourceType
along with their constructors. These errors will be raised by the
upcoming AuthorizeBatch path and carry enough structured fields for
GraphQL/MCP wrappers to map them to user-facing error codes.
Cover their Error() formatting alongside the existing single-resource
authorization errors.
Signed-off-by: Bryan Frimin <bryan@probo.com>
