Fix: remove custom fonts, add launcher icons

- Remove JetBrainsMono font assets (using google_fonts instead)
- Add adaptive icon and PNG fallbacks for launcher
- Build successful: app-release.apk (23.7MB)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

android/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="@color/ic_launcher_background"/>
+    <foreground android:drawable="@drawable/ic_launcher_foreground"/>
+</adaptive-icon>