Refresh h2bc static form parity

[chubes4]

Summary

• Refresh the bundled h2bc dependency to consume the static form surrogate parity fix from Fix static form surrogate parity html-to-blocks-converter#421.
• Prefer the root Composer h2bc raw handler and capability functions before older globally loaded prefixed copies.

Dependency

• Depends on Fix static form surrogate parity html-to-blocks-converter#421.

Testing

• composer build
• BFB smoke tests pass after rebuilding the prefixed vendor bundle.

AI assistance

• AI assistance: Yes
• Tool(s): OpenCode (GPT-5.5)
• Used for: Drafted the dependency refresh and handler-precedence fix; Chris remains responsible for review and validation.