feat(network): draw.io XML import

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

frontend/src/components/network/DiagramHeader.tsx

@@ -1,6 +1,6 @@
 import { useState, useCallback, useRef, useEffect } from 'react'
 import { useNavigate } from 'react-router-dom'
-import { ChevronLeft, Save, Download, FileJson, FileCode, Image, FileText, Undo2, Redo2, MousePointer2, Hand, Share2 } from 'lucide-react'
+import { ChevronLeft, Save, Download, FileJson, FileCode, Image, FileText, Undo2, Redo2, MousePointer2, Hand, Share2, Upload } from 'lucide-react'
 import { cn } from '@/lib/utils'
 
 export type InteractionMode = 'select' | 'pan'
@@ -19,6 +19,7 @@ interface DiagramHeaderProps {
   onExportPdf: () => void
   onExportJson: () => void
   onExportDrawio: () => void
+  onImportDrawio: () => void
   onUndo: () => void
   onRedo: () => void
   canUndo: boolean
@@ -41,6 +42,7 @@ export function DiagramHeader({
   onExportPdf,
   onExportJson,
   onExportDrawio,
+  onImportDrawio,
   onUndo,
   onRedo,
   canUndo,
@@ -199,6 +201,14 @@ export function DiagramHeader({
         {isSaving ? 'Saving...' : 'Save'}
       </button>
 
+      <button
+        onClick={onImportDrawio}
+        className="flex items-center gap-1.5 rounded border border-default px-3 py-1.5 text-xs text-primary hover:border-hover"
+      >
+        <Upload size={14} />
+        Import
+      </button>
+
       <div className="relative" ref={exportMenuRef}>
         <button
           onClick={() => setShowExportMenu(prev => !prev)}