feat: Implement Jupiter-style trading interface with token selection

- Add 'You're paying' and 'You're receiving' sections with proper token dropdowns
- Implement balance display and MAX button functionality
- Add automatic receiving amount calculation based on paying amount
- Enhance token selector with icons, names, and balance information
- Improve leverage position value calculations and risk warnings
- Update trade execution to use new paying/receiving token structure
- Maintain all existing functionality including stop loss, take profit, and position management

This creates a more intuitive and professional trading interface that matches Jupiter's UX patterns.

app/not-found.tsx

@@ -0,0 +1,21 @@
+'use client'
+import React from 'react'
+import Link from 'next/link'
+
+export default function NotFound() {
+  return (
+    <div className="min-h-screen bg-gray-900 flex items-center justify-center">
+      <div className="text-center">
+        <h1 className="text-6xl font-bold text-white mb-4">404</h1>
+        <h2 className="text-2xl font-semibold text-gray-300 mb-8">Page Not Found</h2>
+        <p className="text-gray-400 mb-8">The page you're looking for doesn't exist.</p>
+        <Link 
+          href="/"
+          className="bg-blue-600 hover:bg-blue-700 text-white font-medium py-3 px-6 rounded-lg transition-colors"
+        >
+          Go Back Home
+        </Link>
+      </div>
+    </div>
+  )
+}