feat: update Docker configuration and CI/CD workflows for local image builds

docker-compose.prod.yml

@@ -20,9 +20,7 @@ services:
 
   # ── Backend (Spring Boot) ────────────────────────────────────────────────────
   backend:
-    build:
-      context: ./backend
-      dockerfile: Dockerfile
+    image: condado-newsletter-backend:latest
     restart: always
     depends_on:
       postgres:
@@ -55,11 +53,7 @@ services:
 
   # ── Frontend + Nginx ─────────────────────────────────────────────────────────
   nginx:
-    build:
-      context: ./frontend
-      dockerfile: Dockerfile
-      args:
-        VITE_API_BASE_URL: ${VITE_API_BASE_URL}
+    image: condado-newsletter-frontend:latest
     restart: always
     ports:
       - "80:80"