Implement Better Auth integration with rate limiting and enhanced security

[Copilot]

This PR addresses the authentication complexity and security concerns by implementing Better Auth as a modern, comprehensive authentication solution and adding rate limiting to protect against abuse.

🔒 Security Enhancements

Rate Limiting Protection

• Login attempts: 5 requests per minute per IP (excludes successful logins)
• Registration attempts: 3 requests per minute per IP
• Admin operations: 5 requests per minute per IP
• User operations: 10 requests per minute per IP
• Automatic cleanup of expired rate limit entries
• Proper HTTP 429 responses with retry-after headers

Better Auth Integration

• Replaced complex JWT session management with Better Auth framework
• Built-in two-factor authentication (2FA) support ready for activation
• Drizzle ORM adapter for seamless PostgreSQL integration
• Type-safe session management with proper TypeScript support

🏗️ Architecture Improvements

Simplified Authentication Middleware

• New withAuth() and withAdminAuth() middleware functions
• Unified authentication patterns across all protected routes
• Enhanced error handling with detailed user feedback
• Maintains backward compatibility with existing user data

Enhanced User Experience

• Better error messages for rate limiting scenarios
• Loading states and improved form validation
• Network error handling with user-friendly messages
• Informative feedback for security events

📋 Key Changes

• API Routes: Updated all protected endpoints to use new middleware
• Frontend: Enhanced login/register forms with better error handling
• Database: Maintained existing schema compatibility
• Security: Added comprehensive rate limiting across all auth endpoints
• Types: Full TypeScript support with proper type definitions

🚀 Production Ready

The implementation requires setting BETTER_AUTH_SECRET environment variable for production. All routes build successfully and maintain backward compatibility with existing user sessions.

Example of rate limiting in action:

// Rate limit configuration per endpoint type
const loginRateLimit = rateLimit({ 
  maxRequests: 5, 
  windowMs: 60000,
  skipSuccessfulRequests: true 
});

This modernizes the authentication system while maintaining the existing user experience and ensuring robust security against common attack vectors.

Fixes #112.

Warning

Firewall rules blocked me from connecting to one or more addresses (expand for details)

I tried to connect to the following addresses, but was blocked by firewall rules:

• fonts.googleapis.com
  • Triggering command: /usr/local/bin/node /home/REDACTED/work/icpc-platform/icpc-platform/node_modules/next/dist/compiled/jest-worker/processChild.js (dns block)
• telemetry.better-auth.com
  • Triggering command: /usr/local/bin/node /home/REDACTED/work/icpc-platform/icpc-platform/node_modules/next/dist/compiled/jest-worker/processChild.js (dns block)

If you need me to access, download, or install something from one of these locations, you can either:

• Configure Actions setup steps to set up my environment, which run before the firewall is enabled
• Add the appropriate URLs or hosts to the custom allowlist in this repository's Copilot coding agent settings (admins only)

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[m10090]

this is wrong.
user.id is a uuid so it is a string and can't be converted to number.