fix(performance): treat a counter/wall-clock type switch as a weakening

Turning `{ value: 100, slack: 10 }` into `{ value: 105, toleranceRatio: 1 }`
skipped the raised-counter-value rule and was reported as a lowered limit.
Switching an entry between counter and wall-clock now needs the
perf-baseline-increase label.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_0166PWobUjpoiWt8E9bBdsCs

docs/architecture/performance-journeys.md

@@ -359,8 +359,9 @@ The job also refuses a weakened baselines file:
 entry's enforced limit (`value × toleranceRatio` or `value + slack`) went up,
 a tolerance or slack widened or an entry disappeared, so a PR cannot grow the
 payload and raise the baseline to match. A counter's `value` may not go up
-either, even when narrower slack lowers its limit. Lowered limits and new
-entries pass.
+either, even when narrower slack lowers its limit, and switching an entry
+between counter and wall-clock (adding or removing `toleranceRatio`) counts
+as a weakening too. Lowered limits and new entries pass.
 
 Baselines only move down. Lower `value` in the same PR as the change that
 earned it, set `updatedAt` and `evidencePr`, and paste the measurement output