Extracted the benchmark YAML export helpers (`yamlEscape` / `formatSettingValue` / `formatSettingsSnapshot`) from the inline `benchmark_results.html` template into a unit-tested module (`static/js/utils/yaml_export.js`, loaded via `<script src>` like the other shared JS utils). No behavior change — it adds regression coverage (`tests/js/utils/yaml_export.test.js`) for the escaping that guards every benchmark YAML download, so a future change to `yamlEscape` can't silently corrupt exports.
