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/node-tooltip.tsx

@@ -0,0 +1,77 @@
+import { createContext, useContext, useState, useCallback, type ReactNode, type ComponentProps } from 'react'
+import { NodeToolbar, type NodeToolbarProps } from '@xyflow/react'
+import { cn } from '@/lib/utils'
+
+interface NodeTooltipContextValue {
+  visible: boolean
+  show: () => void
+  hide: () => void
+}
+
+const NodeTooltipContext = createContext<NodeTooltipContextValue>({
+  visible: false,
+  show: () => {},
+  hide: () => {},
+})
+
+export function NodeTooltip({ children, ...props }: ComponentProps<'div'>) {
+  const [visible, setVisible] = useState(false)
+  const show = useCallback(() => setVisible(true), [])
+  const hide = useCallback(() => setVisible(false), [])
+
+  return (
+    <NodeTooltipContext.Provider value={{ visible, show, hide }}>
+      <div {...props}>{children}</div>
+    </NodeTooltipContext.Provider>
+  )
+}
+
+export function NodeTooltipTrigger({
+  children,
+  onMouseEnter,
+  onMouseLeave,
+  ...props
+}: ComponentProps<'div'>) {
+  const { show, hide } = useContext(NodeTooltipContext)
+
+  return (
+    <div
+      onMouseEnter={(e) => {
+        show()
+        onMouseEnter?.(e)
+      }}
+      onMouseLeave={(e) => {
+        hide()
+        onMouseLeave?.(e)
+      }}
+      {...props}
+    >
+      {children}
+    </div>
+  )
+}
+
+export function NodeTooltipContent({
+  className,
+  position,
+  children,
+  ...props
+}: Omit<NodeToolbarProps, 'children'> & { children: ReactNode }) {
+  const { visible } = useContext(NodeTooltipContext)
+
+  if (!visible) return null
+
+  return (
+    <NodeToolbar
+      position={position}
+      className={cn(
+        'rounded-lg border border-default bg-elevated px-3 py-2',
+        'pointer-events-none',
+        className,
+      )}
+      {...props}
+    >
+      {children}
+    </NodeToolbar>
+  )
+}