Refresh HTML converter snapshot

[chubes4]

Summary

• Refresh the bundled chubes4/html-to-blocks-converter snapshot from 5afe783 to c4f9418.
• Pull in the static nav/menu toggle chrome conversion fix from h2bc PR #419.
• Rebuild vendor_prefixed/ so runtime BFB consumers get the updated converter behavior.

Verification

• php tests/smoke-h2bc-capability-discovery-prefixed.php
• php tests/smoke-h2bc-capability-discovery-standalone.php
• php tests/smoke-scoped-h2bc-hooks.php
• php tests/smoke-content-normalization.php
• for test in tests/smoke-*.php; do php "$test" || exit 1; done

Note: direct php tests/*.php is not valid here because tests/BFBConversionUnitTest.php requires the WordPress unit test harness (WP_UnitTestCase).

AI assistance

• AI assistance: Yes
• Tool(s): OpenCode (GPT-5.5)
• Used for: Refreshed the vendored h2bc snapshot, rebuilt scoped runtime files, and ran standalone smoke verification. Chris remains responsible for review and acceptance.