feat(ext/vault): scaffold vault.html tab with sidebar+pane layout and hash routing

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

extension/manifest.json

@@ -30,5 +30,10 @@
   "content_security_policy": {
     "extension_pages": "script-src 'self' 'wasm-unsafe-eval'; object-src 'self'"
   },
+  "commands": {
+    "open-vault": {
+      "description": "Open relicario vault"
+    }
+  },
   "web_accessible_resources": []
 }