fix(auth): a Google connect names its tab's account too, and a refused tab says why

- /auth/google/connect is a navigation and carries no headers: the tab names the account it
  was built for in `expect`, checked by the same comparison as the request header
  (built_for_another_account); a mismatch lands on /?account=changed
- the link marker names the OAuth state of its own flow: an older flow coming back no longer
  spends the marker of the connect still open (which then returned as a plain sign-in)
- a 401 account_changed reloads the tab with a one-time flag, and the reloaded tab says it
  now shows the account signed in
- a refused switch to a suspended or not-yet-approved account says so in the signed-in
  app's words, naming the address a request was recorded for
- the prefs merge locks FOR NO KEY UPDATE, so a transaction that only added a row referring
  to the account does not hold the save up; a test pins the lock
- giving up a lost page closes a channel page open over it
- e2e README names the chromium-only specs

frontend/e2e/README.md

@@ -25,7 +25,8 @@ that one error again and passes every other failure straight on. Don't run two e
 same machine at once.
 
 **Browsers** — every flow runs in three projects: `chromium` (Desktop Chrome), `webkit` (Desktop
-Safari) and `ipad` (iPad gen 7 landscape: 1080×810, touch, mobile). Install the engines once per
+Safari) and `ipad` (iPad gen 7 landscape: 1080×810, touch, mobile) — except `a11y`, `member` and
+`devices`, which run on chromium only (`CHROMIUM_ONLY`; why is in the `docs/gates.md` row). Install the engines once per
 machine with `npx playwright install chromium webkit`; run one project with
 `npx playwright test --project=ipad`. WebKit catches what every iOS browser inherits from the engine
 (JS, CSS/layout, event order). It does **not** reproduce iPad media refusals: Playwright's WebKit