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

apps/trade-exchange/requirements.txt

@@ -1,5 +1,8 @@
-fastapi==0.104.1
-uvicorn[standard]==0.24.0
-sqlalchemy==2.0.23
-pydantic==2.5.0
-python-multipart==0.0.6
+# AITBC Trade Exchange Requirements
+# Compatible with Python 3.13+
+
+fastapi>=0.111.0
+uvicorn[standard]>=0.30.0
+sqlalchemy>=2.0.30
+pydantic>=2.7.0
+python-multipart>=0.0.6