feat: comprehensive dark theme UI overhaul

[trippusultan]

This commit introduces a complete dark theme redesign with modern aesthetics:

Color Palette:

• Modern dark backgrounds (#0f1419) replacing harsh black
• Sophisticated surface colors for elevation and depth
• Updated primary color to indigo (#6366f1) for modern look
• Enhanced semantic colors (success, warning, danger, info)

Enhanced Components:

• Cards with subtle shadows and improved contrast
• Forms with better input styling and focus states
• Buttons with hover effects and glow shadows
• Alerts with semi-transparent backgrounds
• Tables with improved striping and hover states
• Modals with deep shadows for better depth
• Dropdowns with elevation and smooth interactions

UI Improvements:

• Smooth transitions for all color/background changes
• Custom scrollbar styling for webkit browsers
• Enhanced focus states for accessibility
• Better text selection highlighting
• Improved navigation hover states
• Form validation with dark mode colors
• Toast notifications with themed colors

Interactive Features:

• Animated theme toggle with icon rotation
• Keyboard shortcut (Ctrl/Cmd + D) for quick toggle
• Smooth page transition on theme change
• Enhanced hover effects throughout

Additional Enhancements:

• DataTables dark mode support
• Introjs tutorial styling
• Code blocks with syntax-friendly colors
• Print styles that revert to light mode
• Image opacity adjustments for comfort
• Better contrast ratios for readability

The dark theme now provides a sophisticated, modern user experience that's easy on the eyes while maintaining excellent accessibility.

[nguyenkims]

Thanks, can you put the screenshots of before after please?