Finish the Official Video.js Skill and Plugin

## Context

Video.js needs a portable official skill that teaches agents the product model, documentation lookup order, current terminology, and verification expectations.

## Outcome

Merge the Video.js skill and cross-agent plugin packaging for supported clients.

## References

- https://github.com/videojs/skills/pull/1
- https://app.notion.com/p/3e297a7f89d081868510c0d717e44f8f