- Add TelegramAuthPayloadBuilder in GmRelay.Shared for C# tests.
- Refactor TelegramAuthServiceTests to use the shared builder.
- Add Python equivalent (telegram_init_data.py) for E2E runner.
- Add self-contained Python tests and E2E README.
Closes#144
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>