invoicing: point app/api at the real registry host

The conversion left the image host as a placeholder (registry-api.example).
Point both containers at the actual registry the built app/api images live in
(novox/invoicing-{app,api}, tags 51-55 + latest present). Tracks :latest to
match the app's continuous-deploy model; pin by digest later if reproducibility
of a specific build is wanted.

Claude-Session: https://claude.ai/code/session_01LrgweAeERJYBg88c5cKDzF

modules/invoicing/module.json

@@ -67,7 +67,7 @@
       "id": "app",
       "type": "container",
       "name": "invoicing-app",
-      "image": "registry-api.example/novox/invoicing-app:latest",
+      "image": "registry-api.novox.be/novox/invoicing-app:latest",
       "network": "invoicing",
       "env": {
         "UID": "2201",
@@ -81,7 +81,7 @@
       "id": "api",
       "type": "container",
       "name": "invoicing-api",
-      "image": "registry-api.example/novox/invoicing-api:latest",
+      "image": "registry-api.novox.be/novox/invoicing-api:latest",
       "network": "invoicing",
       "env": {
         "UID": "2201",