ci(perf): enforce the journey counters stable on master (#1829)

* ci(perf): enforce the journey counters stable on master

Promote the J1, J2 and J3 counters that were identical in all 55 measured
iterations of the 11 master runs from 2026-10-03 to 2026-10-04 to
journey-baselines.json, and check them in the Performance journeys job
(still warn-only), in one step together with #1828's two validated J1
entries. None of the new ones has Principle 3 evidence, so each carries a
"guard only, not validated" note that the checker prints with a failure.
A performance-tools test keeps the job's --only list equal to the journey
entries. Number formatting uses three decimals, the precision of the
layout-shift scores.

J2 renderer.layoutShiftScore is 0.233, not the window's 0.222: every
master run from #1814 (page Back buttons in the header) on reads 0.233.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

* ci(perf): check the journey counters whenever a summary was written

Review follow-up (Greptile): the check ran only after the composite
action succeeded, so a failed job-summary report after a written
summary.json skipped every baseline. It now runs unless the job was
cancelled, as long as the action produced a summary path.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

---------

Co-authored-by: 4gray <fourgray@proton.me>
Co-authored-by: Claude Opus 5.5 <noreply@anthropic.com>

.github/workflows/performance-ratchet.yml

@@ -240,7 +240,7 @@ jobs:
                       git diff "$HEAD_SHA" HEAD -- "$baselines"
                       echo '```'
                       echo
-                      echo "If \`master\` moved since \`$HEAD_SHA\`, make sure the Initial bytes ratchet job passes on this PR before merging."
+                      echo "If \`master\` moved since \`$HEAD_SHA\`, make sure the Initial bytes ratchet and Performance journeys jobs pass on this PR before merging."
                   } > "$BODY"
                   gh api -X PATCH "repos/$REPOSITORY/pulls/$pr" -F "body=@$BODY" --silent
                   echo "Pull request: ${GITHUB_SERVER_URL}/$REPOSITORY/pull/$pr"