feat: ambient silliness across the app (reduced-motion aware)

- Lock screen: full ambient scene above the unlock form (the idle 'screensaver'
  — wallet auto-locks here) instead of a thin banner.
- History ('home'): full scene as a top banner.
- Send/Receive: IdleDoge — a small click-through sitting doge in the corner,
  the 'most quiet' idle for task screens.
- Mining keeps its own scene.
All gated by Config::reducedMotion (scenes freeze, doge shows a still frame).

src/ReceiveWidget.cpp

@@ -12,6 +12,7 @@
 #include "utils/config.h"
 #include "utils/Icons.h"
 #include "utils/Utils.h"
+#include "widgets/IdleDoge.h"
 
 ReceiveWidget::ReceiveWidget(Wallet *wallet, QWidget *parent)
         : QWidget(parent)
@@ -20,6 +21,8 @@ ReceiveWidget::ReceiveWidget(Wallet *wallet, QWidget *parent)
 {
     ui->setupUi(this);
 
+    new IdleDoge(this);   // wowlet: whisper-quiet corner critter (freezes when reduced-motion)
+
     m_model = m_wallet->subaddressModel();
     m_proxyModel = new SubaddressProxyModel(this, m_wallet->subaddress());
     m_proxyModel->setSourceModel(m_model);