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/res/values/colors.xml

@@ -0,0 +1,5 @@
+<?xml version="1.0" encoding="utf-8"?>
+<resources>
+    <!-- Adaptive-icon background: dark indigo so the violet Punktfunk dots pop. -->
+    <color name="ic_launcher_background">#16132A</color>
+</resources>