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/tsconfig.json

@@ -0,0 +1,25 @@
+{
+  "compilerOptions": {
+    "target": "ES2020",
+    "useDefineForClassFields": true,
+    "lib": ["ES2020", "DOM", "DOM.Iterable"],
+    "module": "ESNext",
+    "skipLibCheck": true,
+
+    /* Bundler mode */
+    "moduleResolution": "bundler",
+    "allowImportingTsExtensions": true,
+    "resolveJsonModule": true,
+    "isolatedModules": true,
+    "noEmit": true,
+    "jsx": "react-jsx",
+
+    /* Linting */
+    "strict": true,
+    "noUnusedLocals": true,
+    "noUnusedParameters": true,
+    "noFallthroughCasesInSwitch": true
+  },
+  "include": ["src"],
+  "references": [{ "path": "./tsconfig.node.json" }]
+}