feat(model): add Status field and constants to User and File

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>

internal/model/file.go

@@ -4,6 +4,9 @@ import (
 	"time"
 )
 
+// StatusUserDeleted marks a file that has been deleted by the user (soft delete).
+const StatusUserDeleted = "user_deleted"
+
 // File represents a file or directory entry in the virtual filesystem.
 type File struct {
 	ID          string    `gorm:"primaryKey;type:varchar(36)" json:"id"`
@@ -14,6 +17,7 @@ type File struct {
 	MimeType    string    `gorm:"type:varchar(127)" json:"mime_type"`
 	StoragePath string    `gorm:"type:varchar(512)" json:"storage_path"`
 	Hash        string    `gorm:"type:varchar(64)" json:"-"`
+	Status      string    `gorm:"type:varchar(32);not null;default:active;index" json:"-"`
 	IsDir       bool      `gorm:"default:false" json:"is_dir"`
 	CreatedAt   time.Time `json:"created_at"`
 	UpdatedAt   time.Time `json:"updated_at"`