fix: exclude migrations from Docker image to prevent startup crash

The migrations directory was being included in the Docker build context,
causing postgres.js sql.unsafe() to fail on large multi-statement SQL.
Migrations are run externally via deploy.sh as intended.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: createpjf

apps/cloud-gateway/.dockerignore

@@ -12,6 +12,7 @@ nginx.conf
 nginx-init.conf
 monitoring/
 scripts/
+migrations/
 openapi.yaml
 README.md
 *.md