fix: register RLS hook on gateway — agent creation was failing with policy violation

The gateway never called configure_rls_hook(engine), so SET LOCAL
app.current_tenant was never set for any DB operation through the
portal API endpoints. All tenant-scoped writes (agent creation, etc.)
failed with "new row violates row-level security policy."

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

packages/gateway/gateway/main.py

@@ -53,13 +53,17 @@ from shared.api import (
     webhook_router,
 )
 from shared.config import settings
-from shared.db import async_session_factory
+from shared.db import async_session_factory, engine
+from shared.rls import configure_rls_hook
 
 logger = logging.getLogger(__name__)
 
 # ---------------------------------------------------------------------------
 # FastAPI app
 # ---------------------------------------------------------------------------
+# Register RLS hook so tenant context is set for all DB operations
+configure_rls_hook(engine)
+
 app = FastAPI(
     title="Konstruct Channel Gateway",
     description="Unified ingress for all messaging platforms",