feat(platform): Enhance SDK authorization with required client_secret and improved authentication flow
- Make client_secret a required field in SdkAuthorization instead of optional
- Update authentication logic to check for Authorization header and use SdkAuthorizationAuth when present
- Add Authorization header-based authentication in payment methods listing and connector session endpoints
- Remove v1/v2 feature flag check in get_ephemeral_or_other_auth to unify authentication flow
- Improve error handling with proper validation for missing client_secret
Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>