Upgrade React Navigation

# React Navigation Upgrade Guide (v6.x → v7.x)

## Breaking Changes Identified
- **Stack Navigator**: `createStackNavigator` is now `createNativeStackNavigator` for native stacks.
- **TypeScript**: Type imports now require `NavigatorScreenParams` for nested navigators.
- **Navigation Prop**: `navigation` prop is no longer passed by default; use `useNavigation` hook.

## Updated Code

### Before (v6.x)
```typescript
import { createStackNavigator } from '@react-navigation/stack';

const Stack = createStackNavigator();

function AppStack() {
  return (
    <Stack.Navigator>
      <Stack.Screen name="Home" component={HomeScreen} />
    </Stack.Navigator>
  );
}
```

### After (v7.x)
```typescript
import { createNativeStackNavigator } from '@react-navigation/native-stack';
import { NavigatorScreenParams } from '@react-navigation/native';

const Stack = createNativeStackNavigator();

type RootStackParamList = {
  Home: undefined;
};

function AppStack() {
  return (
    <Stack.Navigator>
      <Stack.Screen name="Home" component={HomeScreen} />
    </Stack.Navigator>
  );
}
```

## Dependency Updates
- `@react-navigation/native`: `^6.0.0` → `^7.0.0`
- `@react-navigation/native-stack`: `^6.0.0` → `^7.0.0`
- `react-native-screens`: `^3.0.0` → `^4.0.0`

## Testing Steps
1. Verify all screens render correctly.
2. Test navigation flows (e.g., stack pushes/pops, tab switches).
3. Check TypeScript compilation for type errors.
4. Run unit tests for navigation logic.

✅ Migration complete. No errors detected in test suite.