refactor(cli): remove empty yarn.lock workaround

--no-immutable via --no-frozen-lockfile handles yarn's hardened mode,
making the empty yarn.lock creation unnecessary.

Author: fengmk2

packages/cli/src/migration/migrator.ts

@@ -1126,14 +1126,6 @@ function rewriteYarnrcYml(projectPath: string): void {
     // catalog
     rewriteCatalog(doc);
   });
-
-  // Ensure yarn.lock exists so yarn install can update it in CI.
-  // Yarn Berry's hardened mode on public PRs forbids lockfile *creation*
-  // but allows *updating* an existing one.
-  const yarnLockPath = path.join(projectPath, 'yarn.lock');
-  if (!fs.existsSync(yarnLockPath)) {
-    fs.writeFileSync(yarnLockPath, '');
-  }
 }
 
 /**