feat: Docker multi-stage build and CI/CD push

Improve Docker to multi-stage build and push to registry.

• Update central pipeline reference to main.

.gitlab-ci.yml

+# Comment to trigger build = 26
+
 variables:
   CONTAINER_IMAGE: "graphpolaris/frontend"
+  IMAGE_TAG_HELM_FILE: "/helm/staging/graphpolaris-frontend/values.yaml"
+  IMAGE_TAG_HELM_FILE_VARIABLE: "image.tag"
 
 include:
   - project: 'graphpolaris/pipelines'