feat(frontend): add React dashboard with TypeScript

Add modern React frontend to replace Streamlit dashboard:
- Vite build system with TypeScript
- Tailwind CSS for styling
- Component structure in src/
- Production Dockerfile with nginx
- Development server on port 5173

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

frontend/src/index.css

@@ -0,0 +1,34 @@
+@tailwind base;
+@tailwind components;
+@tailwind utilities;
+
+body {
+  font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, 'Helvetica Neue', Arial, sans-serif;
+  -webkit-font-smoothing: antialiased;
+  -moz-osx-font-smoothing: grayscale;
+}
+
+/* Custom scrollbar */
+::-webkit-scrollbar {
+  width: 8px;
+  height: 8px;
+}
+
+::-webkit-scrollbar-track {
+  background: #1e293b;
+}
+
+::-webkit-scrollbar-thumb {
+  background: #6366f1;
+  border-radius: 4px;
+}
+
+::-webkit-scrollbar-thumb:hover {
+  background: #4f46e5;
+}
+
+/* Selection */
+::selection {
+  background: rgba(99, 102, 241, 0.3);
+  color: #f8fafc;
+}