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>

res/lang/de.json

@@ -1020,6 +1020,7 @@
     "lite_hide_wipe": "Ausblenden & löschen",
     "lite_import": "Importieren",
     "lite_import_key_label": "Schlüssel importieren",
+    "lite_key_import_failed": "Schlüssel konnte nicht importiert werden — prüfen Sie ihn, entsperren Sie die Wallet (falls verschlüsselt) und versuchen Sie es erneut.",
     "lite_key_imported": "Schlüssel importiert — führen Sie eine Synchronisierung durch, um den Verlauf zu scannen",
     "lite_lock_failed": "Sperren fehlgeschlagen",
     "lite_lock_now": "Jetzt sperren",