docs: CLAUDE.md's CI table omits six jobs, including the one that gates CI's own decision logic

[jhgaylor]

CLAUDE.md's CI pipeline table documents 12 of the 19 jobs in
.github/workflows/ci.yml. #2020 rebuilt the table after #1413 split
sdk-clients, but deliberately kept scope to the rows that had gone wrong
rather than adding the ones that were never there. These omissions predate it.

Measured on 97bcf1a6:

Job id	Check name a red build shows
workflow-checks	CI policy and alert tests
already-tested	Skip the re-run when a PR already tested this exact tree
core-distribution	Core distribution boots without the extensions
compose-fresh-clone	Compose fresh-clone check
compose-pinned-image-boot	Compose boots the pinned image
docs	Docs

(coverage also has no row of its own, but the test row describes it, so it
is not really undocumented.)

Why this matters, and which one to do first

The table's stated purpose is in the sentence above it: "the job name in a red
build tells you which toolchain to go and look at." That promise fails for any
job not in the table.

workflow-checks is the one worth adding first. It runs
python3 -m unittest discover -s scripts/ci, which is the suite that gates the
CI decision logic itself — gate.py, sdk_changes.py, require-checks.py and
their tests. Someone who breaks one of those sees a failing check called
CI policy and alert tests, a name that appears nowhere in the table, and the
job also runs scripts/conflict-markers.py and the alert-fixture evaluation
(#1927, #1939), so the name does not obviously point at scripts/ci/ either.

already-tested is the second most useful, because a reader who sees it
skipped needs to know that is normal on a pull_request and that the probe
only runs on push and merge_group.

Suggested shape

One row each, in the same style as the existing rows: what it runs, plus the
one fact a reader cannot get from the workflow. For workflow-checks that is
"the suite that gates CI's own decision logic"; for already-tested, which
events it runs on and what a skip means.

Related: #1413 (the split), #2020 (the table rebuild that set this scope aside).