feat: add React Flow UI foundation components for network diagrams

BaseNode (structured node shell with header/content/footer slots),
BaseHandle (styled connection handle), LabeledHandle (handle with
port label), NodeStatusIndicator (status border effect),
NodeTooltip (hover details via NodeToolbar).

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

frontend/src/components/network/ui/labeled-handle.tsx

@@ -0,0 +1,39 @@
+import type { ComponentProps } from 'react'
+import { type HandleProps, Position } from '@xyflow/react'
+import { cn } from '@/lib/utils'
+import { BaseHandle } from './base-handle'
+
+const flexDirections: Record<string, string> = {
+  [Position.Top]: 'flex-col',
+  [Position.Right]: 'flex-row-reverse justify-end',
+  [Position.Bottom]: 'flex-col-reverse justify-end',
+  [Position.Left]: 'flex-row',
+}
+
+export function LabeledHandle({
+  className,
+  labelClassName,
+  handleClassName,
+  title,
+  position,
+  ...props
+}: HandleProps &
+  ComponentProps<'div'> & {
+    title: string
+    handleClassName?: string
+    labelClassName?: string
+  }) {
+  const { ref, ...handleProps } = props
+  return (
+    <div
+      title={title}
+      className={cn('relative flex items-center', flexDirections[position], className)}
+      ref={ref}
+    >
+      <BaseHandle position={position} className={handleClassName} {...handleProps} />
+      <label className={cn('text-muted-foreground text-[10px] font-mono px-1.5', labelClassName)}>
+        {title}
+      </label>
+    </div>
+  )
+}