fix(lite): lock/unlock parity — shared attempt-lockout, immediate unlock state, no dead PIN, surfaced encrypt failure

Lite-parity audit, FIX C (gating/validation/presentation only — no encrypt/unlock/send backend call changed):
- Lite unlock went straight to the backend with no lockout. New App::unlockLiteWallet() runs the SAME
  escalating, persisted attempt-lockout as the full node (restoreLockoutState/applyUnlockFailure), wired into
  the Settings unlock, the send-time prompt and the lock screen. A wrong-passphrase failure counts; an
  already-unlocked/not-encrypted result does not.
- state_.locked is now cleared immediately on a successful unlock (the ~2s status poll lagged, so the UI
  stayed "locked" after a correct passphrase).
- PIN quick-unlock controls are hidden in lite Settings — lite has no PIN vault, so they were dead.
- A create/restore whose passphrase encryption FAILS now raises a one-shot visible error
  (takeEncryptionFailureNotice -> lite_encrypt_failed_unencrypted) instead of only a log line; the wallet is
  left open but unencrypted. Fixed the flag on BOTH the lifecycle and the direct create/restore encrypt paths.
- A background sync save is skipped while an encrypted wallet is unlocked (the backend save re-locks it),
  resuming once locked.

Compile- and unit-verified (testLiteWalletControllerLockUnlockParity covers the save-deferral + encrypt-failure
notice, run twice for the flaky guard); the lock-screen lockout/PIN-hiding UX itself is runtime/GUI-only and
not exercised here — worth a manual lite GUI pass.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/util/i18n.cpp

@@ -1354,6 +1354,7 @@ void I18n::loadBuiltinEnglish()
         strings_["lite_unlock_btn"] = "Unlock";
         strings_["lite_unlock_ok"] = "Wallet unlocked — you can send now";
         strings_["lite_unlock_failed"] = "Unlock failed — wrong passphrase?";
+        strings_["lite_encrypt_failed_unencrypted"] = "Wallet encryption failed — your wallet may still be UNENCRYPTED. Open Settings > Security and set the passphrase again.";
 
         // Send Tab
         strings_["pay_from"] = "Pay From";