feat(gateways): Introduce gateway model and update agent provisioning templates

backend/app/schemas/__init__.py

@@ -1,6 +1,7 @@
 from app.schemas.activity_events import ActivityEventRead
 from app.schemas.agents import AgentCreate, AgentRead, AgentUpdate
 from app.schemas.boards import BoardCreate, BoardRead, BoardUpdate
+from app.schemas.gateways import GatewayCreate, GatewayRead, GatewayUpdate
 from app.schemas.metrics import DashboardMetrics
 from app.schemas.tasks import TaskCreate, TaskRead, TaskUpdate
 from app.schemas.users import UserCreate, UserRead, UserUpdate
@@ -13,6 +14,9 @@ __all__ = [
     "BoardCreate",
     "BoardRead",
     "BoardUpdate",
+    "GatewayCreate",
+    "GatewayRead",
+    "GatewayUpdate",
     "DashboardMetrics",
     "TaskCreate",
     "TaskRead",