feat: enhance Unsplash integration with pagination, random images, and portrait orientation
- Added pagination support to search endpoint with page parameter and orientation control (defaults to portrait)
- Implemented new /random endpoint for fetching random portrait images with configurable count
- Enhanced UnsplashPickerComponent with infinite scroll, loading states, and automatic random image loading on open
- Added debounced search input, scroll detection for pagination, and improved error
- Integrated Unsplash API for image search functionality with environment configuration
- Added new Nimbus Editor page component with navigation from sidebar and mobile drawer
- Enhanced TOC with highlight animation for editor heading navigation
- Improved CDK overlay z-index hierarchy for proper menu layering
- Removed obsolete logging validation script
