fix: scale replicas in response, K8s metrics client, quota precheck, auth tests

- Add GetMetrics method to MetricsClient interface and implement cluster metrics API
- Add QuotaPrecheck service for validating resource quotas before deployment
- Add auth DTO with role/permission models and auth handler tests
- Add instance diagnostics: mounted NFS volumes, labels, annotations in pod diagnostics
- Update workspace handler with GetWorkspace endpoint and shared-user list
- Fix monitoring handler to use correct service method name
- Add tail_lines fallback in instance handler for snake_case query params
- Update nginx config for SSE log streaming support (no buffering)
- Add comprehensive test coverage: auth_service_test, auth_handler_test,
  auth_dto_test, metrics_client_test, quota_precheck_test
- Update error messages for quota validation and instance operations
- ModifyModal: fix YAML lineWidth:0, modified keys summary, delta-only submit
- InstanceCard: correctly disable scale-minus when replicas <= 0
- SidebarLayout: add hover transition for sidebar items
- Update todo.md and lessons.md with latest fixes

backend/internal/domain/repository/workspace_repository.go

@@ -11,12 +11,14 @@ type WorkspaceRepository interface {
 	GetByID(ctx context.Context, id string) (*entity.Workspace, error)
 	GetByName(ctx context.Context, name string) (*entity.Workspace, error)
 	Update(ctx context.Context, workspace *entity.Workspace) error
+	Delete(ctx context.Context, id string) error
 	List(ctx context.Context) ([]*entity.Workspace, error)
 }
 
 type WorkspaceClusterBindingRepository interface {
 	Upsert(ctx context.Context, binding *entity.WorkspaceClusterBinding) error
 	Get(ctx context.Context, workspaceID, clusterID string) (*entity.WorkspaceClusterBinding, error)
+	ListByWorkspace(ctx context.Context, workspaceID string) ([]*entity.WorkspaceClusterBinding, error)
 	Delete(ctx context.Context, workspaceID, clusterID string) error
 }