fix(ci): include acceptance scripts in backend checks

Supply repository scripts as a named build context for the backend check stage so containerized regression tests can import the same acceptance helpers as local tests. Keep operator scripts out of the runtime image.

deploy/Dockerfile.backend

@@ -10,6 +10,7 @@ COPY . .
 RUN uv sync --locked --no-dev
 
 FROM base AS check
+COPY --from=project-scripts . /scripts/
 RUN uv sync --locked && uv run pytest && uvx ruff==0.14.14 check --select F,E9,B src tests
 
 FROM base AS browser-download