chore: codify backend local verification

scripts/verify-node-version.mjs

@@ -0,0 +1,26 @@
+import { readFileSync } from 'node:fs';
+import { fileURLToPath } from 'node:url';
+import { dirname, resolve } from 'node:path';
+
+const root = resolve(dirname(fileURLToPath(import.meta.url)), '..');
+const packageJson = JSON.parse(readFileSync(resolve(root, 'package.json'), 'utf8'));
+const nvmVersion = readFileSync(resolve(root, '.nvmrc'), 'utf8').trim();
+const expectedMajor = nvmVersion.replace(/^v/, '').split('.')[0];
+const expectedEngine = `${expectedMajor}.x`;
+
+if (packageJson.engines?.node !== expectedEngine) {
+  throw new Error(
+    `Node runtime contracts disagree: .nvmrc=${nvmVersion}, package.json engines.node=${packageJson.engines?.node ?? 'missing'}`,
+  );
+}
+
+const actualVersion = process.versions.node;
+const actualMajor = actualVersion.split('.')[0];
+if (actualMajor !== expectedMajor) {
+  console.error(
+    `Unsupported Node.js runtime: expected ${expectedEngine}, actual ${actualVersion}. Activate .nvmrc before running repository checks.`,
+  );
+  process.exit(1);
+}
+
+console.log(`Node.js runtime verified: ${actualVersion} (${expectedEngine})`);