feat: add dagre auto-layout button

Install dagre for hierarchical graph layout. New toolbar button
applies dagre layout to device nodes based on their connections,
then recalculates site containers to wrap their children.

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

frontend/package.json

@@ -27,6 +27,8 @@
     "@antv/x6-plugin-snapline": "^2.1.7",
     "@ngrx/signals": "^19.2.1",
     "@primeng/themes": "^19.1.4",
+    "@types/dagre": "^0.7.53",
+    "dagre": "^0.8.5",
     "primeicons": "^7.0.0",
     "primeng": "^19.1.4",
     "rxjs": "~7.8.0",