Refactor to Hilt dependency injection for RecommendationService

Overview

Migrates RecommendationService from manual DI to Hilt for better testability and cleaner code.

Changes

• Created NetworkModule with Hilt annotations
• Migrated RecommendationViewModel to use @HiltViewModel
• Removed manual DI boilerplate
• Added OkHttp interceptor for auth token injection

Benefits

• Easier to write unit tests with test modules
• Reduced boilerplate code by ~40%
• Better separation of concerns
• Standardized DI approach across the app

Testing

• All existing unit tests pass
• Added new tests for NetworkModule
• Verified recommendation loading in app

Closes #11 (closed)

@stanhu FYI we are standardizing on Hilt across the Android app