Pinned the lockfile check to .nvmrc instead of the floating lts/* alias

setup-node's lts/* already resolves to a different Node major than the
deployed runtime and would silently jump to Node 26 at the next LTS
switch, so the frozen-lockfile install was being validated on a Node
version nobody ships. Reading .nvmrc keeps the check on the same
version as the Dockerfile.

Author: sagzy

.github/workflows/build.yml

@@ -53,7 +53,7 @@ jobs:
       - name: Set up Node.js
         uses: actions/setup-node@820762786026740c76f36085b0efc47a31fe5020 # v7
         with:
-          node-version: lts/*
+          node-version-file: .nvmrc
           cache: pnpm
 
       - name: Check pnpm-lock.yaml