scaffold: add project CI and Docker templates under templates/project/_shared; update proposal and plan to include them

templates/project/_shared/docker/compose.yml

@@ -0,0 +1,19 @@
+name: project
+
+services:
+  tests:
+    build:
+      context: ..
+      dockerfile: docker/test/Dockerfile
+    container_name: project-tests
+    working_dir: /work
+    volumes:
+      - ..:/work:Z
+    command: ["/bin/bash", "-lc", "scripts/test.sh"]
+    networks:
+      - project-net
+
+networks:
+  project-net:
+    name: project-net
+

templates/project/_shared/docker/test/Dockerfile

@@ -0,0 +1,11 @@
+FROM debian:bookworm-slim
+
+ENV DEBIAN_FRONTEND=noninteractive
+RUN apt-get update \
+    && apt-get install -y --no-install-recommends \
+       ca-certificates git bash curl jq yq \
+       bats \
+    && rm -rf /var/lib/apt/lists/*
+
+WORKDIR /work
+