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
refactor: compact block context menu styling and improve visual density
- Reduced menu width from 240px to 220px and decreased padding throughout for more compact layout
- Scaled down button sizes (p-2 → p-1.5), gaps (gap-3 → gap-2.5), and font sizes (text-base → text-sm)
- Shrunk color picker swatches from 7x7 to 5x5 with thinner ring borders for cleaner appearance
- Tightened spacing in toolbars, submenus, and all menu sections while maintaining usability
- Added opacity property binding
