Add passkey authentication sample to auth quickstart

[macastelaz]

For additional details, please see go/firebase-auth-web-passkey-public-preview.

[gemini-code-assist]

Code Review

This pull request introduces Passkey authentication to the Firebase Auth quickstart, adding a new HTML interface, TypeScript logic utilizing Firebase's passkey APIs, and an updated dependency version. Feedback on the changes highlights two critical issues: first, the local path aliases added to auth/vite.config.js will break builds for external users and should be removed; second, calling JSON.stringify directly on the Firebase User object in auth/passkey.ts will throw a circular structure error, so user.toJSON() should be used instead.