Handle misindented comments and preserve serialization

[bsutton]

Summary

• fix parsing when a comment appears at a lower indentation level than expected before a child key
• keep that misindented comment attached to the subsequent YAML element
• preserve the original comment indentation when writing back pubspec.yaml
• avoid duplicate line ownership during section rendering
• add support for additional documented top-level pubspec keys:
  • funding
  • false_secrets
  • topics
  • ignored_advisories
  • screenshots
• ignore local .mcp_logs/ artifacts

Validation

• formatted changed files with Dart MCP dart_format
• ran full suite with Dart MCP run_tests and all tests passed