Fix R image build by including the lockfile in the Docker context

[Copilot]

The build-and-push Actions job for the R environment was failing before dependency restore began because the Docker build could not find the R lockfile in its build context. This updates the R image build to consume the repository lockfile directly and ensures that file is not excluded by .dockerignore.

• Build context

  • Allow the root renv.lock into the Docker build context.
  • Keep the context narrowly scoped; only the required lockfile is added.

• R Dockerfile

  • Copy renv.lock from the repository root instead of the .devcontainer/r path.
  • Remove the dependency on the devcontainer symlink path during image builds.

• Result

  • The R image build no longer fails on:

    COPY .devcontainer/r/renv.lock renv.lock

  • It now uses:

    COPY renv.lock renv.lock