Add better-auth to Authentication

[jstmrby]

Better Auth gained immense traction over the past year, so it's a worthwhile addition

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Thank you for contributing to the Node.js Toolbox catalog! 🙏

Note: Node.js Toolbox is specifically for backend libraries. If a library works both in the browser AND in Node.js feel free to add it. Libraries that work ONLY in the browser are out of scope for now.

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• To use the exact package name as it appears on NPM (and npm install <package-name>)
• The packages are listed in alphabetical order
• The package doesn't already exist in a different category
• Description doesn't have a dot (.) at the end
• To format with Prettier before committing (npm run prettier)

[Maximization]

Thank you @jstmrby! 🙏 Better Auth now added to Authentication category https://nodejstoolbox.com/categories/authentication