feat: add Docker node type, group rect border style, and categorized node type selector

- Fix DockerNode default icon: use Anchor instead of Package
- Add border_style option to Group Rectangle (solid/dashed/dotted/double/none)
- Group node type selector by category (Hardware, Virtualization, IoT, Generic)
- Add tests for border style feature

frontend/src/utils/__tests__/nodeIcons.test.ts

@@ -28,6 +28,7 @@ describe('ICON_REGISTRY', () => {
     expect(keys).toContain('play')      // Jellyfin
     expect(keys).toContain('shield')    // Pi-hole
     expect(keys).toContain('anchor')    // Portainer
+    expect(keys).toContain('package')   // Docker Host
     expect(keys).toContain('key')       // Vaultwarden
     expect(keys).toContain('database')  // DB services
     expect(keys).toContain('cctv')      // IP Camera / CCTV