feat: scale instances, --reuse-values, values diff, UI redesign, hover animations

Backend (Phase 1):
- Add ScaleInstance endpoint (POST /clusters/{id}/instances/{id}/scale)
- Add GetInstanceValuesDiff endpoint (GET .../values-diff)
- Enable ReuseValues=true in Helm Upgrade for --reuse-values behavior
- Add GetValues/GetChartDefaultValues to HelmClient interface
- Add ScaleInstanceRequest/Response and InstanceValuesDiffResponse DTOs

Frontend (Phase 2):
- InstanceCard: +/- scale buttons with loading spinner
- ModifyModal: values diff view (current vs defaults), Use Defaults button
- ArtifactBrowserPage: collapsible sidebar, compact tag grid, search filter
- TagCard: "LATEST" badge, compact layout, responsive design
- InstanceCard: compact 3-column layout, fewer scrolls needed
- InstancesManagementPage: 3-column grid, compact view
- Global hover-lift and hover-glow CSS utilities
- SidebarNav: subtle hover transition on links

backend/internal/domain/service/instance_service.go

@@ -9,6 +9,7 @@ import (
 	"time"
 
 	"github.com/google/uuid"
+	"github.com/ocdp/cluster-service/internal/adapter/input/http/dto"
 	"github.com/ocdp/cluster-service/internal/domain/entity"
 	"github.com/ocdp/cluster-service/internal/domain/repository"
 	"github.com/ocdp/cluster-service/internal/pkg/authz"
@@ -417,6 +418,80 @@ func (s *InstanceService) StreamInstanceLogs(ctx context.Context, clusterID, ins
 	return streamer.StreamPodLogs(ctx, cluster, instance.Namespace, podName, containerName, tailLines)
 }
 
+// ScaleInstance 扩缩容实例（修改 replicaCount 后执行 Helm upgrade）
+func (s *InstanceService) ScaleInstance(ctx context.Context, clusterID, instanceID string, replicas int, workload string) (*entity.Instance, error) {
+	principal, err := authz.RequirePrincipal(ctx)
+	if err != nil {
+		return nil, entity.ErrUnauthorized
+	}
+	instance, err := s.instanceRepo.GetByID(ctx, instanceID)
+	if err != nil {
+		return nil, entity.ErrInstanceNotFound
+	}
+	if !s.canWriteInstance(principal, instance) {
+		return nil, entity.ErrForbidden
+	}
+	cluster, err := s.clusterRepo.GetByID(ctx, clusterID)
+	if err != nil {
+		return nil, entity.ErrClusterNotFound
+	}
+
+	// Get existing Helm values and patch replicaCount
+	vals, err := s.helmClient.GetValues(ctx, cluster, instance.Name, instance.Namespace)
+	if err != nil {
+		return nil, fmt.Errorf("failed to get current values: %w", err)
+	}
+	if vals == nil {
+		vals = make(map[string]interface{})
+	}
+	vals["replicaCount"] = replicas
+
+	instance.SetValues(vals)
+	instance.BeginOperation(entity.OperationUpgrade, fmt.Sprintf("Scaling to %d replicas", replicas))
+	if err := s.instanceRepo.Update(ctx, instance); err != nil {
+		return nil, err
+	}
+
+	go s.executeAndSyncUpgrade(context.Background(), instance.ID, cluster, nil, instance)
+	return instance, nil
+}
+
+// GetInstanceValuesDiff 获取实例当前 values 与 chart 默认 values 的差异
+func (s *InstanceService) GetInstanceValuesDiff(ctx context.Context, clusterID, instanceID string) (*dto.InstanceValuesDiffResponse, error) {
+	principal, err := authz.RequirePrincipal(ctx)
+	if err != nil {
+		return nil, entity.ErrUnauthorized
+	}
+	instance, err := s.instanceRepo.GetByID(ctx, instanceID)
+	if err != nil {
+		return nil, entity.ErrInstanceNotFound
+	}
+	if !s.canReadInstance(principal, instance) {
+		return nil, entity.ErrInstanceNotFound
+	}
+	cluster, err := s.clusterRepo.GetByID(ctx, clusterID)
+	if err != nil {
+		return nil, entity.ErrClusterNotFound
+	}
+
+	current, err := s.helmClient.GetValues(ctx, cluster, instance.Name, instance.Namespace)
+	if err != nil {
+		return nil, err
+	}
+
+	// Get default values from the chart archive
+	chartPath := s.chartArchivePath(instance)
+	defaults, err := s.helmClient.GetChartDefaultValues(chartPath)
+	if err != nil {
+		return nil, fmt.Errorf("failed to read chart defaults: %w", err)
+	}
+
+	return &dto.InstanceValuesDiffResponse{
+		Current:  current,
+		Defaults: defaults,
+	}, nil
+}
+
 func (s *InstanceService) canReadInstance(principal *authz.Principal, instance *entity.Instance) bool {
 	if principal.IsAdmin() {
 		return true