Add customizable toolbox icons and streamline package integrations

[jazelly]

Summary

• Add toolbox icon customization with cropping, shortcuts, schema validation, and selection tooling.
• Update core, Next.js, Vite, and Webpack integrations and documentation.
• Improve CI, release workflows, smoke tests, and playground coverage.

Testing

• Add and update unit, integration, end-to-end, and release smoke tests.