test(gates): the repo-root scripts are linted and format-checked

scripts/check-node-modules.mjs and gen-changelog.mjs run in check and release but sat outside
every lane: the eslint and prettier lanes run from frontend/, and an ESLint config cannot reach
past its own directory. A contract test now holds them to the js-configs bar (recommended rules
under Node, the frontend's Prettier style); an unused variable and the old formatting are each
red. 0 lint hits; both files reformatted. Registered in docs/gates.md.

scripts/check-node-modules.mjs

@@ -27,7 +27,9 @@ for (const [path, entry] of Object.entries(lock.packages ?? {})) {
   }
   const installed = JSON.parse(readFileSync(manifest, "utf8")).version;
   if (installed !== entry.version)
-    problems.push(`mismatch  ${path.slice(13)}: installed ${installed}, lock pins ${entry.version}`);
+    problems.push(
+      `mismatch  ${path.slice(13)}: installed ${installed}, lock pins ${entry.version}`,
+    );
 }
 
 if (problems.length) {
@@ -37,4 +39,6 @@ if (problems.length) {
   console.error("Fix: cd frontend && npm ci");
   process.exit(1);
 }
-console.log(`node_modules matches package-lock.json (${Object.keys(lock.packages).length - 1} entries)`);
+console.log(
+  `node_modules matches package-lock.json (${Object.keys(lock.packages).length - 1} entries)`,
+);