fix(image): image named with dashes like the stack, the slug stays snake_case

template/{{ part_dir }}/Makefile.jinja

@@ -1,5 +1,5 @@
 COMPOSE := {% if layout == 'part' %}cd .. && {% endif %}docker compose
-IMAGE := {{ project_slug }}/{{ part }}
+IMAGE := {{ project_slug | replace('_', '-') }}/{{ part }}
 changed = ! git diff --quiet $(1) -- $(2) 2>/dev/null
 stamp = { git update-ref $(1) HEAD 2>/dev/null || true; }