Integrate G15 submodules with Debian 13 packaging and devcontainer

.devcontainer/compose.yaml

@@ -0,0 +1,9 @@
+services:
+  dev:
+    image: g15-packaging:latest
+    build:
+      context: ../packaging
+      dockerfile: Dockerfile
+    command: ["sleep", "infinity"]
+    volumes:
+      - ..:/work