Add Nixpacks config with Node 22 and npm install

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

.nixpacks.toml

@@ -0,0 +1,11 @@
+[phases.setup]
+nixPkgs = ["nodejs-22_x"]
+
+[phases.install]
+cmd = "npm install"
+
+[phases.build]
+cmd = "npm run build"
+
+[start]
+cmd = "npm start"