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/rest/instance_handler.go

@@ -371,6 +371,49 @@ func (h *InstanceHandler) StreamInstanceLogs(w http.ResponseWriter, r *http.Requ
 	}
 }
 
+// ScaleInstance 扩缩容实例
+func (h *InstanceHandler) ScaleInstance(w http.ResponseWriter, r *http.Request) {
+	vars := mux.Vars(r)
+	clusterID := vars["cluster_id"]
+	instanceID := vars["instance_id"]
+
+	var req dto.ScaleInstanceRequest
+	if err := json.NewDecoder(r.Body).Decode(&req); err != nil {
+		respondError(w, http.StatusBadRequest, "Invalid request body", err.Error())
+		return
+	}
+	if req.Replicas < 0 {
+		respondError(w, http.StatusBadRequest, "Invalid replicas", "replicas must be >= 0")
+		return
+	}
+
+	result, err := h.instanceService.ScaleInstance(r.Context(), clusterID, instanceID, req.Replicas, req.Workload)
+	if err != nil {
+		respondServiceError(w, err, "Failed to scale instance")
+		return
+	}
+
+	respondJSON(w, http.StatusOK, dto.ScaleInstanceResponse{
+		Instance: convertInstanceResponse(result, true),
+		Replicas: req.Replicas,
+		Message:  fmt.Sprintf("Scaled to %d replicas", req.Replicas),
+	})
+}
+
+// GetInstanceValuesDiff 获取实例 values 差异
+func (h *InstanceHandler) GetInstanceValuesDiff(w http.ResponseWriter, r *http.Request) {
+	vars := mux.Vars(r)
+	clusterID := vars["cluster_id"]
+	instanceID := vars["instance_id"]
+
+	diff, err := h.instanceService.GetInstanceValuesDiff(r.Context(), clusterID, instanceID)
+	if err != nil {
+		respondServiceError(w, err, "Failed to get values diff")
+		return
+	}
+	respondJSON(w, http.StatusOK, diff)
+}
+
 func convertInstanceEntry(entry *entity.InstanceEntry) *dto.InstanceEntryResponse {
 	portResponses := make([]dto.InstanceEntryPortResponse, 0, len(entry.Ports))
 	for _, port := range entry.Ports {