Update app icon

New launcher icon from IconKitchen: adaptive icon layers now live in
mipmap-* (already padded for the safe zone, so the 16% inset wrapper is
gone) and the old drawable-* launcher layers are removed. assets/icon
sources updated to match; app_icon.png is the 512px Play Store icon.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

android/app/src/main/res/mipmap-anydpi-v26/ic_launcher.xml

@@ -1,14 +1,6 @@
 <?xml version="1.0" encoding="utf-8"?>
 <adaptive-icon xmlns:android="http://schemas.android.com/apk/res/android">
-  <background android:drawable="@drawable/ic_launcher_background"/>
+  <background android:drawable="@mipmap/ic_launcher_background"/>
-  <foreground>
+  <foreground android:drawable="@mipmap/ic_launcher_foreground"/>
-      <inset
+  <monochrome android:drawable="@mipmap/ic_launcher_monochrome"/>
-          android:drawable="@drawable/ic_launcher_foreground"
-          android:inset="16%" />
-  </foreground>
-  <monochrome>
-      <inset
-          android:drawable="@drawable/ic_launcher_monochrome"
-          android:inset="16%" />
-  </monochrome>
 </adaptive-icon>