npm package: publish backgrounds as installable package

[alvinreal]

Summary

Publish the background components as an npm package so users can npm install openbackgrounds instead of copy-pasting.

Requirements

• Package name: openbackgrounds (or scoped @openbackgrounds/vue)
• Tree-shakeable exports (import individual backgrounds)
• TypeScript types for props
• Peer dependencies: vue, three, simplex-noise
• README with installation and usage examples
• Automated publish via CI on tagged releases

Context

Copy-paste is great for getting started, but an npm package is essential for production use and wider adoption.