add simple Uberspace deployment option (simpler than Cloudflare)

Instead of the complex Cloudflare Worker setup with CORS proxy,
you can now deploy both PWA and backend on Uberspace (~5€/month).

Changes:
- Add Express.js backend server (server/index.js)
- Update ConfigService to support VITE_API_URL env variable
- Make base path configurable via VITE_BASE_PATH
- Add comprehensive Uberspace deployment guide
- Add .env.production.example for configuration

Deployment options:
1. Uberspace (recommended): Simple, all-in-one hosting
2. GitHub Pages + Cloudflare Workers: Free but complex setup

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

vite.config.ts

@@ -23,7 +23,9 @@ const apiMiddlewarePlugin = {
 };
 
 export default defineConfig({
-	base: "/whattoplay/",
+	// GitHub Pages: /whattoplay/
+	// Uberspace: /
+	base: process.env.VITE_BASE_PATH || "/whattoplay/",
 	plugins: [react(), apiMiddlewarePlugin],
 	server: {
 		port: 5173,