feat(android): adaptive launcher icon with Material You themed-icon support

Replace the placeholder system icon with the Punktfunk brand mark (two overlapping violet circles,
from the shared logo in clients/apple/.../punktfunk_Logo.icon).

- drawable/ic_launcher_foreground.xml: the violet logo (3 exact paths) scaled + centered into the
  108dp adaptive-icon safe zone via a group transform.
- drawable/ic_launcher_monochrome.xml: single-tone silhouette for Android 13+ themed icons
  (Material You) — the launcher recolors it to the wallpaper.
- mipmap-anydpi-v26/ic_launcher{,_round}.xml: adaptive-icon (background + foreground + monochrome);
  dark-indigo background (@color/ic_launcher_background) so the violet pops.
- Manifest: android:icon=@mipmap/ic_launcher + roundIcon (was @android:drawable/sym_def_app_icon).

minSdk 31 → anydpi-v26 covers every device (no legacy PNG mipmaps needed). Verified on a physical
phone (Android 16): the icon renders centered + circle-masked; the themed-icon layer is wired.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

clients/android/app/src/main/AndroidManifest.xml

@@ -27,7 +27,8 @@
 
     <application
         android:allowBackup="false"
-        android:icon="@android:drawable/sym_def_app_icon"
+        android:icon="@mipmap/ic_launcher"
+        android:roundIcon="@mipmap/ic_launcher_round"
         android:label="@string/app_name"
         android:supportsRtl="true"
         android:theme="@style/Theme.PunktfunkAndroid">