Boot splash with the InfoFlow logo instead of the Raspberry Pi one

Own plymouth theme (logo centred on white), quiet kernel command line
without boot text, Raspberry logos or cursor, and no firmware rainbow
square. The initramfs is only rebuilt when the theme changes;
uninstall.sh restores the previous theme.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

config/plymouth/voxip-kiosk/voxip-kiosk.plymouth

@@ -0,0 +1,8 @@
+[Plymouth Theme]
+Name=voxip-kiosk
+Description=VoxIP Kiosk boot splash (logo on white)
+ModuleName=script
+
+[script]
+ImageDir=/usr/share/plymouth/themes/voxip-kiosk
+ScriptFile=/usr/share/plymouth/themes/voxip-kiosk/voxip-kiosk.script

config/plymouth/voxip-kiosk/voxip-kiosk.script

@@ -0,0 +1,12 @@
+# VoxIP Kiosk boot splash: logo.png centred on white, at most half the screen.
+# Replace logo.png (any size, PNG with transparency) for a different logo.
+Window.SetBackgroundTopColor(1, 1, 1);
+Window.SetBackgroundBottomColor(1, 1, 1);
+
+logo = Image("logo.png");
+scale = Math.Min(Window.GetWidth() * 0.5 / logo.GetWidth(), Window.GetHeight() * 0.5 / logo.GetHeight());
+if (scale > 1) scale = 1;
+logo = logo.Scale(logo.GetWidth() * scale, logo.GetHeight() * scale);
+
+sprite = Sprite(logo);
+sprite.SetPosition((Window.GetWidth() - logo.GetWidth()) / 2, (Window.GetHeight() - logo.GetHeight()) / 2, 0);