Replace vite preview with proper HTTP server

frontend/Dockerfile

@@ -17,4 +17,4 @@ RUN npm run build
 
 EXPOSE 5173
 
-CMD ["sh", "-c", "npm run preview -- --host 0.0.0.0 --port ${PORT:-5173}"]
+CMD ["node", "server.js"]

frontend/server.js

@@ -0,0 +1,72 @@
+import http from "http";
+import fs from "fs";
+import path from "path";
+import { fileURLToPath } from "url";
+
+const __dirname = path.dirname(fileURLToPath(import.meta.url));
+const DIST = path.join(__dirname, "dist");
+const PORT = process.env.PORT || 5173;
+
+const MIME_TYPES = {
+  ".html": "text/html; charset=utf-8",
+  ".js": "application/javascript; charset=utf-8",
+  ".mjs": "application/javascript; charset=utf-8",
+  ".css": "text/css; charset=utf-8",
+  ".json": "application/json; charset=utf-8",
+  ".png": "image/png",
+  ".jpg": "image/jpeg",
+  ".jpeg": "image/jpeg",
+  ".gif": "image/gif",
+  ".svg": "image/svg+xml",
+  ".webp": "image/webp",
+  ".ico": "image/x-icon",
+  ".woff": "font/woff",
+  ".woff2": "font/woff2",
+  ".ttf": "font/ttf",
+  ".otf": "font/otf",
+  ".txt": "text/plain; charset=utf-8",
+};
+
+const server = http.createServer((req, res) => {
+  // Strip query string
+  const urlPath = req.url.split("?")[0];
+  let filePath = path.join(DIST, urlPath);
+
+  // Prevent directory traversal outside dist
+  if (!filePath.startsWith(DIST)) {
+    res.writeHead(403);
+    res.end("Forbidden");
+    return;
+  }
+
+  // Try the exact path, then index.html inside a directory, then SPA fallback
+  const tryPaths = [filePath, path.join(filePath, "index.html"), path.join(DIST, "index.html")];
+
+  const tryNext = (paths) => {
+    if (paths.length === 0) {
+      res.writeHead(404);
+      res.end("Not Found");
+      return;
+    }
+
+    const candidate = paths[0];
+    fs.stat(candidate, (err, stat) => {
+      if (err || stat.isDirectory()) {
+        tryNext(paths.slice(1));
+        return;
+      }
+
+      const ext = path.extname(candidate).toLowerCase();
+      const contentType = MIME_TYPES[ext] || "application/octet-stream";
+
+      res.writeHead(200, { "Content-Type": contentType });
+      fs.createReadStream(candidate).pipe(res);
+    });
+  };
+
+  tryNext(tryPaths);
+});
+
+server.listen(PORT, "0.0.0.0", () => {
+  console.log(`Frontend server listening on http://0.0.0.0:${PORT}`);
+});