fix(js): add missing @returns JSDoc to consumer-before-provider fixture

The js-consumer-before-provider fixture was missing a JSDoc @returns
annotation on getUser(), preventing the scope-based resolution pipeline
from propagating the return type and resolving u.save() to User#save.

Mirrors the same pattern already applied to js-cross-file/src/models.js,
and matches how the TypeScript equivalent uses an explicit `: User` return
type annotation.

Fixes the CI test failure introduced when JavaScript was added to
MIGRATED_LANGUAGES in the JS scope-resolution migration (PR #1640).

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

gitnexus/test/fixtures/cross-file-binding/js-consumer-before-provider/b-provider.js

@@ -2,6 +2,7 @@ export class User {
   save() {}
 }
 
+/** @returns {User} */
 export function getUser() {
   return new User();
 }