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/app.h

@@ -333,6 +333,10 @@ public:
     // Lock the lite wallet AND immediately tear down the chat session (the lite backend `lock`
     // doesn't update state_.locked until the next poll, so chat secrets would otherwise linger).
     bool lockLiteWallet();
+    // Unlock the lite wallet with the same escalating attempt-lockout as the full node (persisted across restarts)
+    // and set state_.locked=false right away on success (the poll lags). Takes the passphrase by value and wipes
+    // it. On failure *err (if given) holds a user-facing reason ("Unlock failed..." or the lockout wait).
+    bool unlockLiteWallet(std::string passphrase, std::string* err = nullptr);
     // (Re)build the lite controller from current settings so a changed lite-server selection
     // takes effect. No-op on non-lite/unlinked builds; preserves a live wallet (see app.cpp).
     void rebuildLiteWallet(bool force = false);