feat(xiaoyunque): publish shared-runtime companion

[smackgg]

What changed

• publishes the XiaoYunque companion as a minified Bun bundle instead of a bun build --compile standalone executable
• marks the bundle with the exact #!/usr/bin/env convax-bun header
• documents the shared-runtime companion convention

Why

The standalone build duplicated an entire Bun runtime in this one plugin. The release artifact is now about 64 KB instead of roughly 63.5 MB and is executed by a compatible Convax host's existing app-owned Bun runtime.

Impact

Plugin package 0.3.3, companion 0.3.1, and Registry sequence 22 already exist on the current main line; this PR changes the release build that produces the companion asset.

Validation

• XiaoYunque typecheck and 106 tests
• complete companion build, including source-built FFmpeg
• 12 Registry/companion tests
• Registry sequence 22 validation
• actual MCP initialize through the Bun runtime shipped in /Applications/Convax Dev.app