Fix three critical issues: Docker healthcheck, USD->EUR pricing, static asset caching

- Docker healthcheck: Use Node.js instead of curl (not installed in slim image)
- Pricing: Change from USD ($) to EUR (€) in frontend and backend Stripe integration
- Static assets: Add Cache-Control headers (1 day) for /public and /docs files

src/index.ts

@@ -172,10 +172,17 @@ ${apiKey ? `
 
 // Landing page
 const __dirname = path.dirname(fileURLToPath(import.meta.url));
-app.use(express.static(path.join(__dirname, "../public"), { maxAge: "1h", etag: true }));
+app.use(express.static(path.join(__dirname, "../public"), { 
+  maxAge: "1d", 
+  etag: true,
+  setHeaders: (res) => {
+    res.setHeader('Cache-Control', 'public, max-age=86400');
+  }
+}));
 
 // Docs page (clean URL)
 app.get("/docs", (_req, res) => {
+  res.setHeader('Cache-Control', 'public, max-age=86400');
   res.sendFile(path.join(__dirname, "../public/docs.html"));
 });