feat: add custom app icon for Android and iOS

[jvsena42]

Summary

Add a custom app icon for the Worn app, replacing the default Android launcher icons and adding the iOS app icon. The icon was designed in the project's Pencil design file and exported for both platforms.

Changes

• Replace default Android vector drawable launcher icons (PNG/XML) with new WebP adaptive icons including foreground, background, and monochrome variants for all density buckets
• Add Android launcher background color resource
• Add iOS app icon (1024x1024 PNG) with AppIcon asset catalog entry
• Add Play Store high-res icon (ic_launcher-playstore.png)
• Update adaptive icon XML to reference new foreground/monochrome/background layers
• Update design file with app icon design

Test plan

• Install on Android device/emulator and verify the launcher icon displays correctly (regular, round, and monochrome/themed variants)
• Build and run on iOS simulator/device and verify the app icon appears correctly on the home screen
• Verify adaptive icon works with different launcher shapes (circle, squircle, rounded square)

Checklist

• ./gradlew detekt passes
• Tested on Android
• Tested on iOS
• Updated documentation (if applicable)

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