fix: add nixpacks.toml to force Node 22 on Railway

Author: ralyodio

nixpacks.toml

@@ -0,0 +1,11 @@
+[phases.setup]
+nixPkgs = ["nodejs_22", "pnpm"]
+
+[phases.install]
+cmds = ["pnpm install --frozen-lockfile"]
+
+[phases.build]
+cmds = ["pnpm build"]
+
+[start]
+cmd = "pnpm start"