Update Python version requirements and fix compatibility issues

- Bump minimum Python version from 3.11 to 3.13 across all apps
- Add Python 3.11-3.13 test matrix to CLI workflow
- Document Python 3.11+ requirement in .env.example
- Fix Starlette Broadcast removal with in-process fallback implementation
- Add _InProcessBroadcast class for tests when Starlette Broadcast is unavailable
- Refactor API key validators to read live settings instead of cached values
- Update database models with explicit

packages/py/aitbc-crypto/README.md

@@ -146,9 +146,29 @@ pytest tests/security/
 ## Dependencies
 
 - **pynacl**: Cryptographic primitives (Ed25519, X25519)
-- **pydantic**: Data validation and serialization
+- **Dependencies**: pynacl>=1.5.0, pydantic>=2.0.0
 - **Python 3.11+**: Modern Python features and performance
 
+## Compatibility & Stability
+
+### Python Version Support
+- **Minimum Version**: Python 3.11+
+- **Recommended**: Python 3.11 or 3.12  
+- **Security Guarantee**: All cryptographic operations maintain security properties
+- **Performance**: Optimized for Python 3.11+ performance improvements
+
+### Cryptographic Security
+- **Algorithm**: Ed25519 digital signatures (constant-time implementation)
+- **Key Security**: 256-bit keys with proper entropy requirements
+- **Signature Verification**: Timing-attack resistant verification
+- **Randomness**: Uses cryptographically secure random number generation
+
+### API Stability
+- **Major Version**: 0.x (pre-1.0, APIs may evolve)
+- **Backward Compatibility**: Maintained within Python 3.11+ versions
+- **Security Updates**: Non-breaking security improvements may be added
+- **Deprecation Notice**: 2+ releases for deprecated cryptographic features
+
 ## License
 
 MIT License - see LICENSE file for details.