fix: show every password error in its own fixed-height line (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. On the add wallet screen the line sits beside the
Import button, which keeps its place at 360x600. 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

@@ -44,6 +44,19 @@ then continue tagging as milestones land.
 
 # 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. On the add wallet screen the line sits beside
+  the Import button, so the button stays where it was at 360x600. 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: Pre-1.0 security review of the extension
   ([#383](https://git.eeqj.de/sneak/AutistMask/issues/383)), reading the tree at
   `99292b9` for key handling, the DEBUG mode policy, and what the background