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
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