feat: Migrate to Material 3 with dynamic theming

This commit migrates the application to a Material 3 based UI with support for dynamic color theming (Material You).

Key changes:
- Added `@pchmn/expo-material3-theme` to get system colors on Android 12+.
- Created a `styles/theme.js` file to provide a dynamic theme to the app via a `useAppTheme` hook.
- Updated `App.js` to use the new dynamic theme with `PaperProvider`.
- Refactored all screens in the `screens` directory to use colors and styles from the dynamic theme, replacing hardcoded values.
- Updated `MainNavigator.js` and `GroupsStackNavigator.js` to use the dynamic theme for the tab bar and headers, ensuring a consistent look and feel.
- Created a `MIGRATION_GUIDE.md` to document the changes.

Author: google-labs-jules[bot]

frontend/frontend/package-lock.json

@@ -10,6 +10,7 @@
   },
   "dependencies": {
     "@expo/metro-runtime": "~5.0.4",
+    "@pchmn/expo-material3-theme": "^1.0.0",
     "@react-native-async-storage/async-storage": "^2.2.0",
     "@react-navigation/bottom-tabs": "^7.4.4",
     "@react-navigation/native": "^7.1.16",