Create GPU service foundation

- Created gpu-service application structure
- Added pyproject.toml with FastAPI, SQLModel, asyncpg, and aitbc-core dependencies
- Implemented main.py with basic GPU service structure
- Created systemd service file for gpu-service (port 8101)
- Added README.md with installation and configuration instructions
- Documented future work needed for full GPU extraction

This starts Phase 4.3: Extract GPU Service (foundation created, full extraction requires additional work)

apps/gpu-service/gpu-service.service

@@ -0,0 +1,17 @@
+[Unit]
+Description=AITBC GPU Service
+After=network.target postgresql.service
+
+[Service]
+Type=simple
+User=aitbc
+WorkingDirectory=/opt/aitbc/apps/gpu-service
+Environment="PATH=/opt/aitbc/venv/bin"
+Environment="PYTHONPATH=/opt/aitbc/packages/py/aitbc-core/src:/opt/aitbc/apps/gpu-service/src:/opt/aitbc"
+Environment="DATABASE_URL=postgresql+asyncpg://aitbc_gpu:password@localhost:5432/aitbc_gpu"
+ExecStart=/opt/aitbc/venv/bin/python -m gpu_service.main
+Restart=always
+RestartSec=10
+
+[Install]
+WantedBy=multi-user.target