Add script to build and push Docker images to registry

- Introduced `push-images.sh` script for building and pushing backend and frontend images.
- Added functionality to select or input image tags.
- Integrated environment variable support for registry configuration.
- Implemented prompts for user confirmation before building and pushing images.
- Updated `docker-compose.prod.yml` with new image tags after pushing.

.env.example

@@ -22,3 +22,10 @@ SMTP_SECURE=false
 
 # Planner limits
 EMAILS_PER_DAY=3
+
+# Container registry (used by scripts/push-images.sh)
+REGISTRY_HOST=git.danielvolz.org
+REGISTRY_TOKEN=
+REGISTRY_USER=  # optional; defaults to token if empty
+PROJECT_PATH=daniel/medassist
+# IMAGE_TAG can stay empty; override via -v flag