feat(US-15): add app icon

Adaptive icon (API 26+) with dark background and lime-yellow
pulse ring + center dot matching the UI aesthetic. Legacy PNG
icons generated at all densities (mdpi through xxxhdpi).

app/src/main/res/drawable/ic_launcher_background.xml

@@ -0,0 +1,10 @@
+<?xml version="1.0" encoding="utf-8"?>
+<vector xmlns:android="http://schemas.android.com/apk/res/android"
+    android:width="108dp"
+    android:height="108dp"
+    android:viewportWidth="108"
+    android:viewportHeight="108">
+    <path
+        android:fillColor="#0A0A0A"
+        android:pathData="M0,0 H108 V108 H0 Z" />
+</vector>

app/src/main/res/drawable/ic_launcher_foreground.xml

@@ -0,0 +1,20 @@
+<?xml version="1.0" encoding="utf-8"?>
+<vector xmlns:android="http://schemas.android.com/apk/res/android"
+    android:width="108dp"
+    android:height="108dp"
+    android:viewportWidth="108"
+    android:viewportHeight="108">
+
+    <!-- Outer ring -->
+    <path
+        android:strokeColor="#E8FF47"
+        android:strokeWidth="4"
+        android:fillColor="@android:color/transparent"
+        android:pathData="M54,20 A34,34 0 1,1 53.999,20 Z" />
+
+    <!-- Center dot -->
+    <path
+        android:fillColor="#E8FF47"
+        android:pathData="M54,46 A8,8 0 1,1 53.999,46 Z" />
+
+</vector>

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

@@ -0,0 +1,5 @@
+<?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" />
+    <foreground android:drawable="@drawable/ic_launcher_foreground" />
+</adaptive-icon>

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

@@ -0,0 +1,5 @@
+<?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" />
+    <foreground android:drawable="@drawable/ic_launcher_foreground" />
+</adaptive-icon>