Fix admin dashboard errors, enable 6-digit PIN (223344), and enhance visual styling

[Copilot]

This PR addresses critical issues in the admin dashboard and implements the requested 6-digit PIN functionality with enhanced visual styling.

🔧 Key Fixes

PIN Standardization (223344)

Fixed inconsistent PIN handling across the application where some components used "2233" while others used "223344". All authentication flows now consistently use the 6-digit PIN "223344":

• Student Login: Updated Auth.tsx to accept 223344 as the default PIN
• Student Profile: Updated security alerts and password change dialogs to reference 223344
• Admin Dashboard: Verified student creation uses 223344 consistently
• Password Reset: Ensured reset functionality uses the 6-digit PIN

Visual Enhancements

Implemented modern gradient backgrounds and improved styling throughout the admin interface:

• Admin Dashboard: Applied beautiful blue-indigo-purple gradient (from-blue-50 via-indigo-50 to-purple-50)
• Student Management: Coordinated indigo-purple-pink gradient (from-indigo-50 via-purple-50 to-pink-50)
• Headers: Enhanced with improved transparency, backdrop blur, and subtle shadows
• Buttons: Added hover effects and gradient styling for better user experience

📱 UI Improvements

Enhanced Admin Dashboard Overview:

Student Creation with 6-digit PIN:

Updated Student Authentication:

✅ Functionality Verified

• Student Creation: Admin can create students with 6-digit PIN (223344)
• Authentication: Students can login using the standardized 6-digit PIN
• Dashboard Navigation: All tabs (Overview, Students, Quick Create, Results, etc.) work perfectly
• Password Management: Reset functionality properly uses 6-digit PIN
• Visual Consistency: Modern gradient backgrounds applied throughout admin interface

🚀 Technical Changes

• src/pages/Auth.tsx: Updated PIN validation and placeholder text to use 223344
• src/pages/StudentProfile.tsx: Updated security alerts and dialog descriptions
• src/pages/AdminDashboard.tsx: Enhanced background gradients and header styling
• src/pages/AdminStudentManagement.tsx: Applied coordinated gradient color scheme

All changes are backward compatible and maintain existing functionality while providing the requested 6-digit PIN support and visual improvements.

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