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/adapter/input/http/dto/instance_dto.go

@@ -206,6 +206,25 @@ type InstanceEventDiagnostics struct {
 	LastTimestamp  string `json:"lastTimestamp,omitempty"`
 }
 
+// ScaleInstanceRequest 扩缩容实例请求
+type ScaleInstanceRequest struct {
+	Replicas int    `json:"replicas" binding:"required"`
+	Workload string `json:"workload"`
+}
+
+// ScaleInstanceResponse 扩缩容实例响应
+type ScaleInstanceResponse struct {
+	Instance *InstanceResponse `json:"instance"`
+	Replicas int               `json:"replicas"`
+	Message  string            `json:"message"`
+}
+
+// InstanceValuesDiffResponse 实例 values 差异响应
+type InstanceValuesDiffResponse struct {
+	Current  map[string]interface{} `json:"current"`
+	Defaults map[string]interface{} `json:"defaults"`
+}
+
 type InstancePodLogResponse struct {
 	Pod       string `json:"pod"`
 	Container string `json:"container"`