Add logo.png (source) and logo.ico (multi-size: 256/128/64/48/32/16)
generated with Pillow. Remove avalonia-logo.ico (Avalonia template
placeholder). Update MainWindow.axaml Icon and csproj ApplicationIcon
to point to the new files.
Adds QRCoder 1.8.0 and generates a PNG QR code in-memory each time
the receive address changes (OnReceiveAddressChanged). The bitmap is
displayed in the Receive tab inside a white-background border with
pixel-perfect scaling (BitmapInterpolationMode=None). Previous bitmap
is disposed to avoid memory leaks.