feat(android): add app logo as launcher icon

Generate mipmap ic_launcher.png at all standard densities (mdpi→xxxhdpi)
from logo.png, cropped to bounding box and scaled to 88% of the tile on
a white background (legacy fallback for API < 26).

For API 26+ provide an adaptive icon (ic_launcher.xml / ic_launcher_round.xml)
with white background and a foreground PNG where the logo occupies 56% of
the 108dp canvas — within the safe zone, fully visible on every launcher
shape without clipping.

src/App.Android/Resources/mipmap-anydpi-v26/ic_launcher.xml

@@ -0,0 +1,5 @@
+<?xml version="1.0" encoding="utf-8"?>
+<adaptive-icon xmlns:android="http://schemas.android.com/apk/res/android">
+    <background android:drawable="@color/ic_launcher_background"/>
+    <foreground android:drawable="@drawable/ic_launcher_foreground"/>
+</adaptive-icon>