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

frontend/src/api/index.ts

@@ -237,6 +237,26 @@ export const getInstance = getClustersClusterIdInstancesInstanceId;
 export const updateInstance = putClustersClusterIdInstancesInstanceId;
 export const deleteInstance = deleteClustersClusterIdInstancesInstanceId;
 export const listInstanceEntries = getClustersClusterIdInstancesInstanceIdEntries;
+export const scaleInstance = (
+  clusterId: string,
+  instanceId: string,
+  body: { replicas: number; workload?: string },
+) => {
+  return customAxiosInstance<{ instance: any; replicas: number; message: string }>({
+    url: `/clusters/${encodeURIComponent(clusterId)}/instances/${encodeURIComponent(instanceId)}/scale`,
+    method: "POST",
+    data: body,
+  });
+};
+export const getInstanceValuesDiff = (
+  clusterId: string,
+  instanceId: string,
+) => {
+  return customAxiosInstance<{ current: Record<string, any>; defaults: Record<string, any> }>({
+    url: `/clusters/${encodeURIComponent(clusterId)}/instances/${encodeURIComponent(instanceId)}/values-diff`,
+    method: "GET",
+  });
+};
 export const getInstanceDiagnostics = (
   params: { clusterId: string; instanceId: string },
   options?: { tailLines?: number },