feat: replace app launcher icon with new PNG-based adaptive icon

Add density-specific mipmap resources (mdpi through xxxhdpi) with
background, foreground, and monochrome PNGs. Update adaptive-icon
XML to reference mipmap drawables and remove unused color resources.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

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

@@ -1,5 +1,6 @@
 <?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"/>
+  <background android:drawable="@mipmap/ic_launcher_background"/>
-    <foreground android:drawable="@color/ic_launcher_foreground"/>
+  <foreground android:drawable="@mipmap/ic_launcher_foreground"/>
+  <monochrome android:drawable="@mipmap/ic_launcher_monochrome"/>
 </adaptive-icon>

android/app/src/main/res/values/ic_launcher_colors.xml

@@ -1,5 +0,0 @@
-<?xml version="1.0" encoding="utf-8"?>
-<resources>
-    <color name="ic_launcher_background">#2196F3</color>
-    <color name="ic_launcher_foreground">#FFFFFF</color>
-</resources>