ci(docker): add postgres image build configuration and update image tags

- Add xingrin-postgres image build job to docker-build workflow for multi-platform support (linux/amd64,linux/arm64)
- Update docker-compose.dev.yml to use IMAGE_TAG variable with dev as default fallback
- Update docker-compose.yml to use IMAGE_TAG variable with required validation
- Replace hardcoded postgres image tag (15) with dynamic IMAGE_TAG for better version management
- Enable flexible image tagging across development and production environments

.github/workflows/docker-build.yml

@@ -44,6 +44,10 @@ jobs:
             dockerfile: docker/agent/Dockerfile
             context: .
             platforms: linux/amd64,linux/arm64
+          - image: xingrin-postgres
+            dockerfile: docker/postgres/Dockerfile
+            context: docker/postgres
+            platforms: linux/amd64,linux/arm64
 
     steps:
       - name: Checkout