feat(network): draw.io XML export

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 } from 'lucide-react'
+import { ChevronLeft, Save, Download, FileJson, FileCode, Image, FileText, Undo2, Redo2, MousePointer2, Hand, Share2 } from 'lucide-react'
 import { cn } from '@/lib/utils'
 
 export type InteractionMode = 'select' | 'pan'
@@ -18,6 +18,7 @@ interface DiagramHeaderProps {
   onExportSvg: () => void
   onExportPdf: () => void
   onExportJson: () => void
+  onExportDrawio: () => void
   onUndo: () => void
   onRedo: () => void
   canUndo: boolean
@@ -39,6 +40,7 @@ export function DiagramHeader({
   onExportSvg,
   onExportPdf,
   onExportJson,
+  onExportDrawio,
   onUndo,
   onRedo,
   canUndo,
@@ -233,6 +235,12 @@ export function DiagramHeader({
                 <FileJson size={12} /> Export JSON
               </button>
             )}
+            <button
+              onClick={() => { onExportDrawio(); setShowExportMenu(false) }}
+              className="flex w-full items-center gap-2 px-3 py-1.5 text-xs text-primary hover:bg-elevated"
+            >
+              <Share2 size={12} /> Export draw.io
+            </button>
           </div>
         )}
       </div>