fix: show every password error in its own line below the field (closes #493)

The add wallet screen reported a missing, short or mismatched password in
the flash line at the top of the popup, and the private key export,
recovery phrase and delete wallet screens each wrote to a line of their own
above the password field. All four now use showError() and hideError() with
a fixed-height error line below the field, as the send confirmation and
approval screens do. The line clears when the screen is shown again and
when the password is tried again. Other add wallet messages stay in the
flash line.

Model: opus-5-5

TODO.md

@@ -45,6 +45,18 @@ but the review is broader than any of them.
 
 # Completed Steps
 
+- 2026-10-07: Every password error in the popup is shown the same way
+  ([#493](https://git.eeqj.de/sneak/AutistMask/issues/493)): with `showError()`
+  and `hideError()` in a fixed-height error line below the password field, as
+  the send confirmation and approval screens already did. The add wallet screen
+  showed a missing, short or mismatched password in the flash line, and the
+  private key export, recovery phrase and delete wallet screens each had a line
+  of their own above the field. Each line clears when the screen is shown again
+  and when the password is tried again. The add wallet screen's other messages,
+  such as an invalid recovery phrase, a duplicate wallet and the address scan,
+  stay in the flash line. `tests/passwordErrorLines.test.js` drives all four
+  screens in the popup.
+
 - 2026-10-07: The README says that the wallet never clears the clipboard after
   the private key or the recovery phrase is copied, and why
   ([#492](https://git.eeqj.de/sneak/AutistMask/issues/492)): the clipboard is