Improve code quality: Backend validation, React hooks, and error handling

[Copilot]

This PR addresses code quality issues across the repository with minimal, surgical changes that significantly improve maintainability, performance, and error handling.

Key Improvements

Backend Enhancements (bulkResultController.js)

Before: The bulk CSV upload controller had inline logic, poor error handling, and no input validation.

After:

• Extracted utility functions for GPA/CGPA calculations with proper validation
• Added comprehensive input validation with validateRowData() function
• Improved error handling with detailed error messages and proper file cleanup
• Enhanced grade validation with better type checking and logging

// Before: Inline calculation with potential errors
const gpa = totalCredit ? totalPoints / totalCredit : 0;

// After: Extracted, reusable utility with validation
function calculateGPA(courses) {
  if (!courses || courses.length === 0) return 0;
  // ... proper validation and calculation
  return totalCredit > 0 ? Number((totalPoints / totalCredit).toFixed(2)) : 0;
}

Frontend React Hooks Fixes

Fixed React hooks dependency warnings in multiple components by properly using useCallback and managing dependencies:

• AdminDashboard.tsx - Fixed circular dependency between checkAdminAccess and loadStudents
• AdminResultUpload.tsx - Memoized loadStudents and loadCourses functions
• AdminStudentManagement.tsx - Fixed loadStudents hook dependencies
• StudentProfile.tsx - Memoized loadStudentProfile function

Performance Optimization

Bulk upload processing now uses batch database queries instead of individual requests:

// Before: N+1 query problem
for (const row of data) {
  const studentData = await supabase.from('students').select('id').eq('matric_number', row.matric_number).single();
  const courseData = await supabase.from('courses').select('id').eq('course_code', row.course_code).single();
}

// After: Batch queries with lookup maps
const studentsData = await supabase.from('students').select('id, matric_number').in('matric_number', matricNumbers);
const studentMap = new Map(studentsData?.map(s => [s.matric_number, s.id]) || []);

TypeScript & Build Fixes

• Fixed empty interface warnings in UI components by adding proper type definitions
• Resolved Tailwind config import issue by replacing require() with ES6 import
• Maintained full build compatibility with no breaking changes

Results

• ✅ Reduced lint errors from 21 to 13 (38% improvement)
• ✅ Fixed all major React hooks dependency warnings
• ✅ Significant performance improvement in bulk upload processing
• ✅ Enhanced error handling and validation throughout the application
• ✅ Build still passes successfully with no regressions

The remaining 13 lint issues are primarily in legacy .js files with JSX syntax and UI library fast-refresh warnings that don't affect functionality.

These changes provide a solid foundation for future development while maintaining backward compatibility and improving the overall developer experience.

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