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/components/canvas/nodes/GroupRectNode.tsx

@@ -31,6 +31,7 @@ export function GroupRectNode({ id, data, selected }: NodeProps<Node<NodeData>>)
 
   const rc = data.custom_colors ?? {}
   const borderColor = rc.border ?? '#00d4ff'
+  const borderStyle = rc.border_style ?? 'solid'
   const backgroundColor = rc.background ?? 'rgba(0,212,255,0.05)'
   const textColor = rc.text_color ?? '#e6edf3'
   const fontFamily = FONT_FAMILIES[rc.font ?? 'inter'] ?? FONT_FAMILIES.inter
@@ -61,7 +62,7 @@ export function GroupRectNode({ id, data, selected }: NodeProps<Node<NodeData>>)
           justifyContent: posStyle.justifyContent,
           padding: 12,
           background: backgroundColor,
-          border: `${selected ? 2 : 1}px solid ${selected ? '#00d4ff' : borderColor}`,
+          border: `${selected ? 2 : 1}px ${selected ? 'solid' : borderStyle} ${selected ? '#00d4ff' : borderColor}`,
           borderRadius: 10,
           fontFamily,
           color: textColor,