Create and publish library documentation and guides

[mridang]

Summary: Created & Published Backend Library Documentation & Examples

What

Clear user guides and an API reference for the zitadel-backend-auth library, alongside all official examples, published to a public Zitadel GitHub repository.

Why

To enable developers to easily adopt and utilize zitadel-backend-auth, providing accessible and version-controlled resources.

Requirements

An example is published with corresponding documentation, clearly explaining how to implement a best-practice Zitadel authentication setup. This includes demonstrating PKCE, back-channel logout, client-side session management, API route protection, and JWKS validation. Repository is public, examples are runnable, and docs are linked/render correctly.