feat: parameterize Docker images in docker-compose-local.yml

[inDane]

What

Adds LB_*_DOCKER_IMAGE and LB_*_DOCKER_TAG environment variables so the DB and app images in docker-compose-local.yml can be overridden without modifying the compose file.

Why

• Pin specific image versions for reproducibility
• Swap registries or use local builds without touching YAML
• Keep the defaults for drop-in compatibility

Variables

Variable	Example-Value
LB_DB_DOCKER_IMAGE	my.registry.example.com/hub.docker.com/linuxserver/mariadb
LB_DB_DOCKER_TAG	10.6.13
LB_APP_DOCKER_IMAGE	my.registry.example.com/hub.docker.com/librebooking/librebooking
LB_APP_DOCKER_TAG	5.1.0
LB_PROXY_DOCKER_IMAGE	my.registry.example.com/hub.docker.com/nginxproxy/nginx-proxy
LB_PROXY_DOCKER_TAG	latest
LB_ACME_DOCKER_IMAGE	my.registry.example.com/hub.docker.com/nginxproxy/acme-companion
LB_ACME_DOCKER_TAG	latest

Backward compatible

• Defaults match the previous hardcoded values — no behavior change for existing users.

[inDane]

forgot to add the env variables to docker-compose-public.yml.