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/coordinator-api/tests/conftest.py

@@ -4,6 +4,10 @@ import sys
 import os
 import tempfile
 from pathlib import Path
+import pytest
+from sqlmodel import SQLModel, create_engine, Session
+from app.models import MarketplaceOffer, MarketplaceBid
+from app.domain.gpu_marketplace import ConsumerGPUProfile
 
 _src = str(Path(__file__).resolve().parent.parent / "src")
 
@@ -23,3 +27,11 @@ os.environ["TEST_MODE"] = "true"
 project_root = Path(__file__).resolve().parent.parent.parent
 os.environ["AUDIT_LOG_DIR"] = str(project_root / "logs" / "audit")
 os.environ["TEST_DATABASE_URL"] = "sqlite:///:memory:"
+
+@pytest.fixture(scope="function")
+def db_session():
+    """Create a fresh database session for each test."""
+    engine = create_engine("sqlite:///:memory:", echo=False)
+    SQLModel.metadata.create_all(engine)
+    with Session(engine) as session:
+        yield session