High-priority fixes:
- Message length validation and splitting (4096 char limit)
- Empty chat_id validation to prevent silent failures
- Health check timeout (5s) to prevent service hangs
Testing infrastructure:
- Comprehensive test suite (20+ automated tests)
- Quick smoke test script
- Test message generator
- Complete testing documentation
All changes are backward compatible.
Co-authored-by: Claude Sonnet 4.5 <noreply@anthropic.com>
