Add landing page, Docker setup, and CI/CD pipeline

React + Vite + TypeScript + Tailwind frontend with landing page,
Docker Compose for dev and prod (nginx-proxy integration),
and Gitea Actions workflow for automated deployment.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

frontend/src/main.tsx

@@ -0,0 +1,10 @@
+import { StrictMode } from 'react';
+import { createRoot } from 'react-dom/client';
+import App from './App';
+import './index.css';
+
+createRoot(document.getElementById('root')!).render(
+  <StrictMode>
+    <App />
+  </StrictMode>,
+);