fix: Back from Settings never lands on Settings itself (closes #481)

The recovery phrase and delete wallet screens take themselves off the
Back stack when left, so Settings, one of those screens, then the
settings gear leaves Settings under the Settings now showing. A reopened
popup restores the same stack, cut at the screen the gear left. Back
then showed Settings again and seemed to do nothing.

goBack() now skips any entry for the screen already showing before it
pops its target. Jest tests drive the gear and then Back for the
recovery phrase screen, once and twice over, for both delete screens,
and after a reopen.

Model: opus-5-5

TODO.md

@@ -45,6 +45,15 @@ but the review is broader than any of them.
 
 # Completed Steps
 
+- 2026-10-07: Back from Settings no longer shows Settings again after the
+  settings gear was pressed on the recovery phrase or a delete wallet screen
+  opened from Settings, with or without a reopen in between
+  ([#481](https://git.eeqj.de/sneak/AutistMask/issues/481)). Those screens take
+  themselves off the Back stack when left, which leaves Settings under Settings;
+  `goBack()` now skips an entry for the screen already showing.
+  `tests/showPhrase.test.js`, `tests/deleteWalletLostPassword.test.js` and
+  `tests/backNavigation.test.js` drive each path.
+
 - 2026-10-07: `script/discard-dist-on-failure` returns the failed step's own
   exit status even when it cannot write its message, to a closed stderr or to a
   pipe nobody reads any more