photos' admin-client, client and server Dockerfiles live in subdirectories and copy
paths from the module's root (admin-client/..., client-server/serve.mjs), as build-agent
built them and as the fingerprint reads the module's whole directory. Taking the
Dockerfile's own directory as context failed every such COPY with copier: stat
"/admin-client/package.json": no such file or directory, on shanks and on ace.
Quick fix (rejected): move photos' Dockerfiles to its repository root; it changes the
operator's photo application and leaves the trap for the next module.
Thorough fix (chosen): one context for every image, the module's directory; it never
leaves that directory, so the isolation of ADR 0487 section 2 holds.