feat(lite): wire send + new-address GUI to the lite controller (M3/M4)

Route the existing receive/balance/send UI to the lite controller in lite builds,
with no per-tab UI changes — the existing buttons just work:

- App::createNewZAddress / createNewTAddress: lite branch calls
  lite_wallet_->newAddress() (synchronous local key derivation), injects the new
  address into WalletState so the UI selects it next frame, and invokes the
  receive-tab callback. Placed before the full-node !connected guard.
- App::sendTransaction: lite branch builds a LiteSendRequest (DRGX -> zatoshis,
  memo; `from`/`fee` ignored since the backend selects inputs and adds the fee),
  fires the controller's async broadcast, and stashes the send_tab callback.
- App::update: drains takeBroadcastResult() and delivers txid/error to the stored
  callback, so the send_tab's existing "sending.../sent" flow works unchanged.

All branches guard on lite_wallet_ (null in full-node). Verified: lite app +
test suite + full-node variant all build/link clean; hygiene clean.

Backup/import UI (export seed/keys, import) is deferred — it needs new
secret-display UI rather than an existing button.

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

src/app.cpp

@@ -407,6 +407,14 @@ void App::update()
         if (lite_wallet_->takeRefreshedModel(liteModel)) {
             wallet::applyLiteRefreshModelToWalletState(liteModel, state_);
         }
+        // Deliver a completed async send/shield result to the waiting send_tab callback.
+        wallet::LiteBroadcastResult broadcast;
+        if (lite_wallet_->takeBroadcastResult(broadcast)) {
+            if (lite_send_callback_) {
+                lite_send_callback_(broadcast.ok, broadcast.ok ? broadcast.txid : broadcast.error);
+                lite_send_callback_ = nullptr;
+            }
+        }
     }
     async_tasks_.reapCompleted();