feat: Complete Sprint 2 - Dashboard, modernized Settings and History

[Co0ob1iee]

Sprint 2 Implementation Complete:

Dashboard & Shell:

• New MainWindow with NavigationView
• Quick action tiles for common operations
• Theme toggle in TitleBar (light/dark)
• Status bar with cloud and update indicators
• Integration with TrayIcon menu

Settings Modernization:

• Rebuilt with NavigationView and 4 categories
• New "Appearance" section with theme preview
• Minimal mode and transparency options
• Better organization and tooltips

History Improvements:

• Responsive grid layout (3 columns)
• Advanced filters (search, category, date range, tags)
• Hover effects on thumbnails
• Inline actions: Edit, Copy Link, Share, Upload, Delete
• Empty state for no screenshots

Toast Notifications:

• ToastNotificationService with in-app animations
• 4 types: Success, Error, Warning, Info
• Fallback to system tray when window closed

Cloud & Update Status:

• Cloud connection status in dashboard
• Automatic update checking on startup
• Update notification button

Documentation:

• Sprint 2 summary with metrics
• Sprint 3 feedback and recommendations

All Sprint 2 tasks completed ✅