fix: Back from Settings no longer lands on a secret screen left by the gear (closes #461)

Leaving the private key export or recovery phrase screen drops the
selection it was showing, but the settings gear had just pushed the
screen onto the Back stack, so Back from Settings landed on a password
prompt that could only fail. Each screen's leave handler now also takes
it off the top of the stack, which is what a reopened popup already does
to these screens. Back from Settings goes to the address screen for the
export screen; for the recovery phrase screen, opened from Settings, it
stays on Settings once, as after a reopen.

Jest tests drive the gear and then Back, and each screen's own Back, for
both screens; leavePrivkeyScreen() in the e2e suite expects the address
screen.

Model: opus-5-5

TODO.md

@@ -45,6 +45,15 @@ but the review is broader than any of them.
 
 # Completed Steps
 
+- 2026-10-06: Back from Settings no longer lands on the private key export or
+  recovery phrase screen after either was left by the settings gear
+  ([#461](https://git.eeqj.de/sneak/AutistMask/issues/461)). Leaving drops the
+  screen's selection, so its leave handler now also takes it off the Back stack,
+  as a reopened popup already does. `tests/exportPrivkey.test.js` and
+  `tests/showPhrase.test.js` drive the gear and then Back, and
+  `leavePrivkeyScreen()` in `tests/e2e/run.js` expects the address screen after
+  Settings.
+
 - 2026-10-06: A token symbol or name read off a contract is no longer stored cut
   between the two halves of an emoji
   ([#458](https://git.eeqj.de/sneak/AutistMask/issues/458)). `lookupTokenInfo()`