feat: Add roadmap navigation to homepage with back button

Changes:
- Homepage: Added roadmap card with indigo/violet gradient
- Changed grid from 3 to 4 columns (responsive: 2 on mobile, 4 on desktop)
- Roadmap page: Added back button to header for easy navigation
- Visual consistency: Matches existing card design patterns

Navigation Flow:
- Homepage → Roadmap card → /roadmap page
- Roadmap page → Back button → Homepage

Files Modified:
- app/page.tsx (navigation grid + roadmap card)
- app/roadmap/page.tsx (back button in header)

app/roadmap/page.tsx

@@ -82,7 +82,18 @@ export default function RoadmapPage() {
       <div className="max-w-6xl mx-auto space-y-8">
         {/* Header */}
         <div className="bg-gray-800/50 backdrop-blur-sm border border-gray-700 rounded-xl p-6">
-          <h1 className="text-3xl font-bold text-white mb-2">🗺️ Trading Bot Roadmap</h1>
+          <div className="flex items-center justify-between mb-4">
+            <h1 className="text-3xl font-bold text-white">🗺️ Trading Bot Roadmap</h1>
+            <a
+              href="/"
+              className="px-4 py-2 bg-gray-700 hover:bg-gray-600 text-white rounded-lg transition-colors flex items-center gap-2"
+            >
+              <svg className="w-5 h-5" fill="none" stroke="currentColor" viewBox="0 0 24 24">
+                <path strokeLinecap="round" strokeLinejoin="round" strokeWidth={2} d="M10 19l-7-7m0 0l7-7m-7 7h18" />
+              </svg>
+              Back to Home
+            </a>
+          </div>
           <p className="text-gray-400">Track development progress and upcoming features</p>
         </div>