test(perf): detach J1's IPC capture before the J2 click

J2 used J1's capture to see pending launch bridge calls while settling,
but its ipcMain listener stayed attached and ran for every bridge call of
the measured click. The capture can now be detached; J2 detaches J1's
right after settling, before the click.

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

docs/architecture/performance-journeys.md

@@ -264,7 +264,9 @@ fails the iteration). Bridge calls in flight come from J1's IPC capture: it
 was installed before the document loaded, and the preload follows every
 traced `start` with exactly one `success` or `error`, so a call that is still
 pending cannot resolve after the click and have its DOM changes or follow-up
-calls counted as J2. The settle is a snapshot, and Playwright's
+calls counted as J2. After settling, J1's capture is detached
+(`detachJourneyMainIpcCapture`), so its listener does not run for every
+bridge call of the measured click. The settle is a snapshot, and Playwright's
 actionability checks run between it and the click. The probe and the IPC
 capture keep counting pre-click activity until the click event itself, and
 the ledger splits at the click stamp. So the record rejects an iteration