fix: the ml artifact was in a second list I never grepped for (4311)

ac70f2a removed the `ml` image but CI went red on six tests:
`tests/test_artifact_identity.py` parametrises over its own
`ARTIFACTS = ("web", "ml", "agent", "extension")`, and every case now hits
the dispatch guard that same commit added.

My miss, and a specific one. I grepped for `fabledcurator-ml` and `ML_PATHS`
and called the survey done — but the artifact is also named as a bare `"ml"`,
which neither pattern finds. Rule 90 (grep pinned tests when changing a
shared symbol) was surfaced to me while I was making the change and I ran a
narrower sweep than it asks for. Lesson #4275 names the shape exactly: an
absence claim is only as good as the search behind it, and a grep that
matched nothing looks identical to a grep that asked the wrong question.

The re-run was done by value, not by name: every occurrence of a bare `ml` in
the repo, then filtering. That distinguishes the two things the token means —
the celery LANE `ml` and the `backend/app/services/ml` package both stay and
account for nearly every hit; only the IMAGE name went. Worth stating in the
test, since the next person to grep will hit the same ambiguity.

Also swept the prose the first pass left describing the old pipeline: "Four
artifacts" (README, ci-requirements), "leaves web and ml alone" (×5 in
build.yml, plus both docs), "CI publishes it alongside the web/ml images"
(agent/README). The run 4896 build-time measurements keep their `ml` number —
that was measured when ml was a real build — with a note saying the name has
since gone.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01LVjrnpQjRgHdvq95rASoiR

agent/README.md

@@ -21,7 +21,7 @@ docker run --rm --gpus all nvidia/cuda:12.4.1-base-ubuntu22.04 nvidia-smi
 ## 1. Get a token
 In FC: **Settings → Tagging → GPU agent → Generate token** (or Rotate). Copy it.
 
-## 2. Pull (CI publishes it alongside the web/ml images)
+## 2. Pull (CI publishes it alongside the web image)
 ```sh
 docker pull git.fabledsword.com/bvandeusen/fabledcurator-agent:latest
 ```