- Add OAuth2 Authorization Code Flow example (py-oauth2-authorization-code/)
  - Complete flow with local callback server for OAuth redirect
  - Token refresh demonstration
  - Production-ready patterns with error handling

- Add OAuth2 Client Credentials Flow example (py-oauth2-client-credentials/)
  - Robot/service account authentication
  - Reusable OAuth2ClientCredentials class with automatic token management
  - Multiple authentication method examples (Basic Auth, body params)

- Add OAuth1 example (py-oauth1/)
  - Legacy authentication support
  - Complete 3-legged OAuth1 flow
  - Migration guidance to OAuth2

- Add AUTH_README.md with:
  - Decision guide for choosing authentication method
  - Quick comparison table
  - Security best practices
  - Troubleshooting guide

- Update main readme.md with authentication section and example index

Each example includes Python script, README with usage instructions,
and requirements.txt for dependencies.

https://planview.projectplace.com/#direct/card/26044157

We shall maintain only Python examples to the auth procedures.
Relevant docs are updated accordingly.