feat: introduce react-hook-kit package

[p-iknow]

Summary

• replace the starter template with the publishable react-hook-kit package
• add React 17/18/19 compatibility fixtures and an Astro docs app
• add Changesets release automation, CI updates, CODEOWNERS, and issue/PR templates

Commit split

• feat: introduce react-hook-kit package
• test: add React compatibility fixtures
• docs: add package documentation site
• ci: add release and contribution workflows

Test Plan

• pnpm check
• git diff --check HEAD