feat: add JianYing editor Registry plugin

[superche]

Summary

• add the jianying-editor v2 Registry Web Plugin using the generic generation/Canvas host contract
• add the Plugin-owned jianying-editor Skill
• add the reviewed convax-jianying-editor-mcp darwin-arm64 companion for draft inspection, short-lived transfer tokens, and fixed-bundle Deep Links
• register Registry sequence 35

Impact

• the Plugin is available through the Registry but is not installed by default
• media input comes only from direct incoming Canvas edges
• JianYing process/draft access and local transfer behavior stay inside the verified companion

Validation

• workspace package build, Registry validation, typecheck, and tests
• 8 JianYing companion contract/service/inspector/transport tests
• JianYing companion build plus Plugin and Skill pack
• Registry sequence 35 index build

Known validation boundary

The all-companion build reached an existing FFmpeg companion smoke timeout. The JianYing companion's own build, tests, and packaging completed successfully.