Add comprehensive debug endpoint to check environment variables

�� Debug Information:
- New /api/debug endpoint with detailed environment info
- Check for DATABASE_URL and JWT_SECRET presence
- Show environment variable keys related to database
- Force fresh deployment with new endpoint name

This will help identify if environment variables are properly configured in Vercel.

api/debug.js

@@ -0,0 +1,18 @@
+export default function handler(req, res) {
+  res.status(200).json({
+    success: true,
+    message: 'Debug endpoint - latest version',
+    timestamp: new Date().toISOString(),
+    method: req.method,
+    environment: process.env.NODE_ENV || 'unknown',
+    vercel_env: process.env.VERCEL_ENV || 'unknown',
+    has_database_url: !!process.env.DATABASE_URL,
+    has_jwt_secret: !!process.env.JWT_SECRET,
+    database_url_length: process.env.DATABASE_URL ? process.env.DATABASE_URL.length : 0,
+    database_url_starts_with: process.env.DATABASE_URL ? 
+      process.env.DATABASE_URL.substring(0, 20) + '...' : 'not set',
+    all_env_keys: Object.keys(process.env).filter(key => 
+      key.includes('DATABASE') || key.includes('JWT') || key.includes('NEON')
+    )
+  });
+}