Add professional React frontend for API testing

- Complete React 18 + TypeScript application
- Modern UI with Lucide icons and CSS animations
- Features:
  * JWT token generation
  * Transaction submission form
  * 5 pre-built test scenarios
  * Real-time results display
  * Responsive design
  * Dark mode ready

Infrastructure:
  * Vite for fast development
  * Axios for HTTP client
  * React hooks for state management
  * CSS3 with CSS variables for theming

Build:
  * Production-optimized build (63KB gzip)
  * TypeScript compilation
  * Vite bundling

Documentation:
  * frontend/README.md - Frontend-specific guide
  * FULLSTACK_GUIDE.md - Complete API + Frontend setup
  * Comprehensive troubleshooting section

Integration:
  * Connects to FastAPI backend on localhost:8000
  * Full REST API consumption
  * Handles JWT authentication
  * Error handling and user feedback

Co-authored-by: Copilot <[email protected]>

frontend/package.json

@@ -0,0 +1,24 @@
+{
+  "name": "payguard-frontend",
+  "private": true,
+  "version": "1.0.0",
+  "type": "module",
+  "scripts": {
+    "dev": "vite",
+    "build": "tsc && vite build",
+    "preview": "vite preview"
+  },
+  "dependencies": {
+    "axios": "^1.7.7",
+    "lucide-react": "^0.408.0",
+    "react": "^18.3.1",
+    "react-dom": "^18.3.1"
+  },
+  "devDependencies": {
+    "@types/react": "^18.3.3",
+    "@types/react-dom": "^18.3.0",
+    "@vitejs/plugin-react": "^4.2.1",
+    "typescript": "^5.4.2",
+    "vite": "^5.0.8"
+  }
+}