fix: show member email instead of UUID in team management

backend/internal/models/tenant.go

@@ -20,6 +20,7 @@ type UserTenant struct {
 	UserID    uuid.UUID `db:"user_id" json:"user_id"`
 	TenantID  uuid.UUID `db:"tenant_id" json:"tenant_id"`
 	Role      string    `db:"role" json:"role"`
+	Email     string    `db:"email" json:"email"`
 	CreatedAt time.Time `db:"created_at" json:"created_at"`
 }