[Bug]: Root CopilotRule receives frontmatter object despite "no frontmatter" comment

[flanny7]

Hello, I always appreciate rulesync.

Problem

In CopilotRule.fromRulesyncRule(), there is a comment stating "no frontmatter for root file", yet a frontmatter object is still passed to the constructor when creating a root rule. The comment and the implementation are inconsistent.

Evidence

In src/features/rules/copilot-rule.ts around line 167–177:

if (root) {
  // Root file: .github/copilot-instructions.md (no frontmatter for root file)
  return new CopilotRule({
    baseDir: baseDir,
    frontmatter: copilotFrontmatter,  // ← passed despite the comment above
    body,
    relativeDirPath: paths.root.relativeDirPath,
    relativeFilePath: paths.root.relativeFilePath,
    validate,
    root,
  });
}

The frontmatter field is passed to the constructor, but when generating the file content (in getFileContent()), root files skip frontmatter serialization:

fileContent: rest.root ? body : stringifyFrontmatter(body, frontmatter),

So the frontmatter is silently discarded at serialization time. While this avoids visible breakage today, the code's intention is unclear and could become a bug source in future refactors.

Expected Behavior

Either:

1. Root rules should pass frontmatter: undefined (or {}) explicitly to match the stated intent, or
2. The comment should be updated to explain why frontmatter is provided but intentionally unused.

Your confirmation would be appreciated.