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

systemd/aitbc-multimodal.service

@@ -0,0 +1,37 @@
+[Unit]
+Description=AITBC Multi-Modal Agent Service (Port 8002)
+Documentation=https://docs.aitbc.bubuit.net
+After=network.target aitbc-coordinator-api.service
+Wants=aitbc-coordinator-api.service
+
+[Service]
+Type=simple
+User=aitbc
+Group=aitbc
+WorkingDirectory=/opt/aitbc/apps/coordinator-api
+Environment=PYTHONPATH=/opt/aitbc/apps/coordinator-api/src
+Environment=PORT=8002
+Environment=SERVICE_TYPE=multimodal
+Environment=LOG_LEVEL=INFO
+ExecStart=/opt/aitbc/.venv/bin/python -m aitbc_multimodal.main
+ExecReload=/bin/kill -HUP $MAINPID
+Restart=always
+RestartSec=10
+StandardOutput=journal
+StandardError=journal
+SyslogIdentifier=aitbc-multimodal
+
+# Security settings
+NoNewPrivileges=true
+PrivateTmp=true
+ProtectSystem=strict
+ProtectHome=true
+ReadWritePaths=/opt/aitbc/logs /opt/aitbc/data
+LimitNOFILE=65536
+
+# Resource limits
+MemoryMax=2G
+CPUQuota=200%
+
+[Install]
+WantedBy=multi-user.target