fix: require Node 22 for Railway build

- Added nixpacksPlan with nodejs_22 to railway.json
- Added .node-version file
- Added engines.node >= 22 to package.json

Author: ralyodio

.node-version

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

package.json

@@ -48,5 +48,8 @@
     "tailwindcss": "^4.2.2",
     "typescript": "^5.9.3",
     "vitest": "^4.1.0"
+  },
+  "engines": {
+    "node": ">=22"
   }
-}
+}

railway.json

@@ -2,7 +2,15 @@
   "$schema": "https://railway.app/railway.schema.json",
   "build": {
     "builder": "NIXPACKS",
-    "buildCommand": "pnpm install --frozen-lockfile && pnpm build"
+    "buildCommand": "pnpm install --frozen-lockfile && pnpm build",
+    "nixpacksPlan": {
+      "providers": ["node"],
+      "phases": {
+        "setup": {
+          "nixPkgs": ["nodejs_22"]
+        }
+      }
+    }
   },
   "deploy": {
     "startCommand": "pnpm start",