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 = 21
-
 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'
-    ref: fix-build-push
+    ref: main
     file: 'docker-build-push.yml'