fix: require Node >= 22 for Next.js 16 on Railway

Nixpacks was using Node 18 which doesn't support Next.js 16.

Author: ralyodio

.node-version

@@ -0,0 +1 @@
+22

package.json

@@ -40,5 +40,8 @@
       "electron",
       "esbuild"
     ]
+  },
+  "engines": {
+    "node": ">=22"
   }
 }