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/drawable/ic_launcher_foreground.xml

@@ -0,0 +1,27 @@
+<?xml version="1.0" encoding="utf-8"?>
+<!--
+  Punktfunk mark: two overlapping violet circles (two "Punkte") with a lighter lens, from the
+  shared brand logo (clients/apple/.../punktfunk_Logo.icon). The source art lives in a 1001x1000
+  space; the group scales + centers it into the adaptive-icon 108dp safe zone (inner ~66dp circle).
+-->
+<vector xmlns:android="http://schemas.android.com/apk/res/android"
+    android:width="108dp"
+    android:height="108dp"
+    android:viewportWidth="108"
+    android:viewportHeight="108">
+    <group
+        android:scaleX="0.105"
+        android:scaleY="0.105"
+        android:translateX="3.57"
+        android:translateY="-0.62">
+        <path
+            android:fillColor="#A79FF8"
+            android:pathData="M403.037,791.672c107.586,0 194.41,-86.824 194.41,-194.41c0,-107.586 -86.824,-194.41 -194.41,-194.41c-107.586,0 -194.41,86.824 -194.41,194.41c0,107.586 86.824,194.41 194.41,194.41Z" />
+        <path
+            android:fillColor="#6C5BF3"
+            android:pathData="M735.276,540.321c76.075,-76.075 76.075,-198.862 0,-274.937c-76.075,-76.075 -198.862,-76.075 -274.937,0c-76.075,76.075 -76.075,198.862 0,274.937c76.075,76.075 198.862,76.075 274.937,0Z" />
+        <path
+            android:fillColor="#D2C9FB"
+            android:pathData="M647.84,590.737c-64.853,17.403 -136.871,0.597 -187.885,-50.416c-51.013,-51.013 -67.819,-123.032 -50.416,-187.885c64.853,-17.403 136.871,-0.597 187.885,50.416c51.013,51.013 67.819,123.032 50.416,187.885Z" />
+    </group>
+</vector>

clients/android/app/src/main/res/drawable/ic_launcher_monochrome.xml

@@ -0,0 +1,24 @@
+<?xml version="1.0" encoding="utf-8"?>
+<!--
+  Themed-icon (Android 13+/Material You) layer: the Punktfunk silhouette in a single tone — the two
+  overlapping circles as one shape. The launcher recolors this to match the wallpaper, so the fill
+  colour here only needs to be opaque. Same geometry/centering as the foreground.
+-->
+<vector xmlns:android="http://schemas.android.com/apk/res/android"
+    android:width="108dp"
+    android:height="108dp"
+    android:viewportWidth="108"
+    android:viewportHeight="108">
+    <group
+        android:scaleX="0.105"
+        android:scaleY="0.105"
+        android:translateX="3.57"
+        android:translateY="-0.62">
+        <path
+            android:fillColor="#1B1B1F"
+            android:pathData="M403.037,791.672c107.586,0 194.41,-86.824 194.41,-194.41c0,-107.586 -86.824,-194.41 -194.41,-194.41c-107.586,0 -194.41,86.824 -194.41,194.41c0,107.586 86.824,194.41 194.41,194.41Z" />
+        <path
+            android:fillColor="#1B1B1F"
+            android:pathData="M735.276,540.321c76.075,-76.075 76.075,-198.862 0,-274.937c-76.075,-76.075 -198.862,-76.075 -274.937,0c-76.075,76.075 -76.075,198.862 0,274.937c76.075,76.075 198.862,76.075 274.937,0Z" />
+    </group>
+</vector>

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

@@ -0,0 +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" />
+    <foreground android:drawable="@drawable/ic_launcher_foreground" />
+    <monochrome android:drawable="@drawable/ic_launcher_monochrome" />
+</adaptive-icon>

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

@@ -0,0 +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" />
+    <foreground android:drawable="@drawable/ic_launcher_foreground" />
+    <monochrome android:drawable="@drawable/ic_launcher_monochrome" />
+</adaptive-icon>

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>