Add argon2 polyfill and unified preview/API startup for admin login.

Node < 24 lacks crypto.argon2Sync; wire @node-rs/argon2 fallback and start Admin API alongside vite preview in local and remote deploy flows.

Co-authored-by: Cursor <cursoragent@cursor.com>

package.json

@@ -8,9 +8,11 @@
     "dev:web": "vite",
     "dev:server": "node server/index.mjs",
     "build": "vite build",
-    "preview": "vite preview"
+    "preview": "node scripts/preview.mjs",
+    "dev:preview": "vite preview"
   },
   "dependencies": {
+    "@node-rs/argon2": "^2.0.2",
     "express": "^4.21.2",
     "mysql2": "^3.22.5",
     "react": "^19.0.0",