feat: ambient scene system + unlock-screen banner (reduced-motion aware)

Reusable SceneWidget (QQuickWidget host) loads scene.qml — dusk sky, tiled
grass, running doge, bouncing WOW coins (slowed per feedback), drifting
money — and feeds it Config::reducedMotion so it freezes to a still when
that's set. First placement: a banner atop the unlock form. Scene rendered
& verified at banner + screensaver aspects via local qml6 harness. Assets
from wow-lite-wallet (friend's). Home banner / idle screensaver / per-tab
idle to follow on the same SceneWidget.

src/widgets/WalletUnlockWidget.cpp

@@ -9,6 +9,7 @@
 
 #include "utils/Utils.h"
 #include "libwalletqt/Wallet.h"
+#include "widgets/SceneWidget.h"
 
 WalletUnlockWidget::WalletUnlockWidget(QWidget *parent, Wallet *wallet)
         : QWidget(parent)
@@ -18,6 +19,13 @@ WalletUnlockWidget::WalletUnlockWidget(QWidget *parent, Wallet *wallet)
     ui->setupUi(this);
     this->reset();
 
+    // wowlet: ambient scene banner above the unlock form (freezes itself into a
+    // still when "Prefer reduced motion" is set).
+    auto *scene = new SceneWidget(this);
+    scene->setMinimumHeight(120);
+    scene->setMaximumHeight(140);
+    ui->verticalLayout->insertWidget(0, scene);
+
     ui->buttonBox->button(QDialogButtonBox::Ok)->setAutoDefault(true);
 
     connect(ui->buttonBox, &QDialogButtonBox::accepted, this, &WalletUnlockWidget::tryUnlock);