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/tenant_kube_client.go

@@ -11,5 +11,12 @@ import (
 type TenantKubeClient interface {
 	EnsureTenant(ctx context.Context, cluster *entity.Cluster, binding entity.TenantBinding) error
 	IssueKubeconfig(ctx context.Context, cluster *entity.Cluster, binding entity.TenantBinding, ttl time.Duration) (*entity.TenantKubeconfig, error)
+	GetResourceQuotaUsage(ctx context.Context, cluster *entity.Cluster, binding entity.TenantBinding) (*ResourceQuotaUsage, error)
 	SuspendTenant(ctx context.Context, cluster *entity.Cluster, binding entity.TenantBinding) error
+	DeleteTenant(ctx context.Context, cluster *entity.Cluster, binding entity.TenantBinding) error
+}
+
+type ResourceQuotaUsage struct {
+	Hard ResourceVector
+	Used ResourceVector
 }