ci: deploy the verified local image

Build and test the Next.js application once with persistent BuildKit caches, smoke-test the immutable runtime image, and activate that same image through the shared production Docker daemon with serialized rollback-safe deployment.

compose.build.yaml

@@ -0,0 +1,7 @@
+services:
+  portfolio-app:
+    image: amiirkhl-portfolio:latest
+    build:
+      context: .
+      dockerfile: Dockerfile
+      target: runtime