[Bug]: js_image_layer does not include repo mapping file in app layer

[jfirebaugh]

What happened?

js_image_layer omits the repo mapping file, so @bazel/runfiles resolution fails inside the resulting container when bzlmod is enabled.

Version

Development (host) and target OS/architectures:

Output of bazel --version: 7.3.1

Version of the Aspect rules, or other relevant rules from your
WORKSPACE or MODULE.bazel file: 1.37.0

Language(s) and/or frameworks involved:

How to reproduce

Via `js_image_layer`, build a container image containing a `js_binary` target with a runfiles dependency, and with bzlmod enabled. The binary can do nothing but:


const runfiles = require('@bazel/runfiles')
runfiles.resolve('<repo name>/<runfile>')

Run the container. It will fail with "Error: could not resolve module /".

If you inspect the container contents (e.g. with dive), you can see that the app layer has no .repo_mapping file.

### Any other information?

_No response_