React18 Upgrade

# React18 Upgrade

> Imported from [github/awesome-copilot](https://github.com/github/awesome-copilot/blob/613efc8c21d9b3ce642dff361d17006cd9967e28/plugins/react18-upgrade) (MIT, commit `613efc8`). This plugin was written by its upstream authors and has **not been reviewed** by AI Development Hub. See the bundled `LICENSE`.

Enterprise React 18 migration toolkit with specialized agents and skills for upgrading React 16/17 class-component codebases to React 18.3.1. Includes auditor, dependency surgeon, class component migration specialist, automatic batching fixer, and test guardian.

Installing this plugin installs:

- 6 agents: `awesome-copilot/react18-auditor`, `awesome-copilot/react18-batching-fixer`, `awesome-copilot/react18-class-surgeon`, `awesome-copilot/react18-commander`, `awesome-copilot/react18-dep-surgeon`, `awesome-copilot/react18-test-guardian`
- 7 skills: `awesome-copilot/react-audit-grep-patterns`, `awesome-copilot/react18-batching-patterns`, `awesome-copilot/react18-dep-compatibility`, `awesome-copilot/react18-enzyme-to-rtl`, `awesome-copilot/react18-legacy-context`, `awesome-copilot/react18-lifecycle-patterns`, `awesome-copilot/react18-string-refs`