feat(CLI): implement better auth detection

[anirudhprmar]

Issue : #114

Summary

• New Feature
  • added better auth detection for CLI which helps with identify block and imports auth from detected existing config file location for retrieving session information.

Summary by CodeRabbit

• New Features
  • CLI initialization now detects Better Auth in your project and, when present, generates an identity handler wired to Better Auth.
  • Generated configuration will include the appropriate auth import when available or a safe stub identify block otherwise, streamlining auth setup during init.