Use the OOTT brand icon as the app launcher icon on all platforms

The app shipped Flutter's default icon on every platform. Add
flutter_launcher_icons (mirroring the existing flutter_native_splash
setup) with an OOTT wordmark on the brand orange (#fe8019) and
regenerate the native icon sets for iOS, Android, macOS, Windows and
web.

Android uses an adaptive icon (orange background + inset transparent
foreground) so the mark survives any launcher mask; the square
full-bleed source is used elsewhere where the platform applies its own
corner mask. Source images live under assets/icon/.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

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

@@ -0,0 +1,9 @@
+<?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>
+      <inset
+          android:drawable="@drawable/ic_launcher_foreground"
+          android:inset="16%" />
+  </foreground>
+</adaptive-icon>

frontend/android/app/src/main/res/values/colors.xml

@@ -0,0 +1,4 @@
+<?xml version="1.0" encoding="utf-8"?>
+<resources>
+    <color name="ic_launcher_background">#fe8019</color>
+</resources>