Take the metrics generator back to one version, and leave test files out of the architecture surface

Two sessions improved the shared metrics generator at the same time, and it ended up in three versions: kessai's on #3621973, audit_trail's on #3620405, and the one on this module's 1.x. A file whose whole point is to be identical in every module cannot be three files.

This brings the union here, so all five carry the same file byte for byte:

• The dirty-tree warning, so regenerating with uncommitted changes says so rather than writing a page that only reproduces from a commit that does not exist yet.
• The architecture surface counted from shipped files in every row, not only the three read from PHP.
• The reason git gives when it cannot list the files.
• A docs link that names no module's branch, pointing at HEAD rather than 1.x.
• The note that the info-file glob is not recursive, so a submodule's info file is never a candidate, and the refusal when a second one exists rather than a guess.

The surface change is the visible one: the table reported Services 205 where there are 199, event subscribers 27 where there are 26, and routes 102 where there are 98. A test-support module is a module: it carries its own info file and can ship services, routes, permissions, a schema and plugins, all of it scaffolding for the suite and none of it surface a site gets. The three rows read from PHP already left them out; the four read from YAML did not.

AI-Generated: Yes (Claude Code was used to help draft this issue summary and to write the change on the merge request. I reviewed and ran the work myself before posting it.)