fix(lite): keep a rejected import key out of the log and Settings

The backend's error for a key it doesn't recognize repeats the key
("'<key>' was not recognized as either a spending key or a viewing
key"). Import passed that text on as its error, so a mistyped private
key was written to the lite log (shown in the Console tab) and to the
Settings status line. A failed import now carries a fixed reason
(unrecognized format, wallet locked, key already exists, could not be
decoded, or rejected), which is all the log records. Settings shows
"Couldn't import the key — check it, unlock the wallet (if encrypted)
and try again." instead, translated in all eight languages.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

src/wallet/lite_wallet_controller.h

@@ -97,7 +97,8 @@ struct LiteBroadcastResult {
     std::string error;
 };
 
-// importKey outcome. `detail` is the backend's (non-secret) confirmation payload.
+// importKey outcome. `detail` is the backend's (non-secret) confirmation payload. `error` is a fixed, non-secret reason,
+// never the backend's text (which can repeat the key).
 struct LiteImportResult {
     bool ok = false;
     std::string detail;