feat: Enhance attendance system with threshold distance, location features, and UI improvementsfeat: Add attendance system enhancements

[dkborntowin200405-netizen]

Enhanced Features for Smart Attendance System

#1. Threshold Distance Setting (20-100 meters)

• Problem: GPS accuracy varies due to weather/network issues
• Solution: Teachers can set allowed distance range (20m strict to 100m lenient)
• Default: 50 meters (balanced setting)
  -Storage: Saved in database per class for consistent validation

#2. Current Location Button for Teachers

• One-click location: Get current GPS position instantly
• Professional map interface: Clean, simplified selection modal
• Manual selection: Still allows precise manual pin placement
• Coordinates display: Shows selected lat/lng for reference

#3. QR Code Reuse Feature

• Problem: Teachers had to regenerate QR codes when navigating away
• Solution: QR codes saved in database, viewable in Previous Classes
• Benefits:
  • Prevents duplicate attendance marking
  • Students use same QR throughout semester
  • Easy access for late-joining students

#4. Class Management Enhancements

• Delete functionality: Remove classes with attendance records
• Confirmation modal: Prevents accidental deletion
• Attendance count: Shows student count per class
• Clean UI: Professional, minimal interface

#5. Technical Improvements

• Fixed lecturer_id mapping between tables
• Enhanced database schema with threshold_meters column
• Improved error handling and user feedback
• Clean, responsive UI matching original design

#Files Modified:

• src/page/ClassSchedule.jsx - Added threshold slider, improved location selection
• src/page/PreviousClass.jsx - Added QR view and delete functionality
• src/component/MapModal.jsx - Simplified with current location button
• src/component/QRCodeModal.jsx - Clean, professional QR display
• src/page/Attendance.jsx - Updated with threshold validation
• Database schema updated with threshold_meters column

#Testing Instructions:

1. Teacher creates class with threshold setting (20-100m)
2. Uses "Current Location" or manual map selection
3. Generates QR code once, can reuse from Previous Classes
4. Students scan QR - system validates within threshold distance
5. Teacher can view attendance and delete classes if needed

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