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>

pubspec.yaml

@@ -41,10 +41,3 @@ dev_dependencies:
 
 flutter:
   uses-material-design: true
-
-  fonts:
-    - family: JetBrainsMono
-      fonts:
-        - asset: assets/fonts/JetBrainsMono-Regular.ttf
-        - asset: assets/fonts/JetBrainsMono-Bold.ttf
-          weight: 700