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/SendWidget.cpp

@@ -11,6 +11,7 @@
 #include "Icons.h"
 #include "libwalletqt/Wallet.h"
 #include "libwalletqt/WalletManager.h"
+#include "widgets/IdleDoge.h"
 
 #if defined(WITH_SCANNER)
 #include "wizard/offline_tx_signing/OfflineTxSigningWizard.h"
@@ -25,6 +26,8 @@ SendWidget::SendWidget(Wallet *wallet, QWidget *parent)
 {
     ui->setupUi(this);
 
+    new IdleDoge(this);   // wowlet: whisper-quiet corner critter (freezes when reduced-motion)
+
     QString amount_rx = R"(^\d{0,8}[\.,]\d{0,12}|(all)$)";
     QRegularExpression rx;
     rx.setPattern(amount_rx);