Add unified content feature: aggregate and deduplicate content from m…

…ultiple providers

- Add UnifiedContentManager to fetch and deduplicate content from all providers
- Create unified content UI with filtering by type, genre, year, and provider
- Add new navigation item 'All Content' in bottom menu
- Show multi-provider indicators for content available from multiple sources
- Implement content deduplication based on title and year
- Add new layouts and adapters for unified content display
- Update strings and navigation configuration