Add Status field (gorm, indexed, default active) to both User and File models.
Add User status constants: StatusActive, StatusAdminDeleted.
Add File status constant: StatusUserDeleted.
Add tests verifying Status field is excluded from JSON serialization.
Ultraworked with [Sisyphus](https://github.com/code-yeongyu/oh-my-openagent)
Co-authored-by: Sisyphus <clio-agent@sisyphuslabs.ai>
