fix: pin Express to v4 to avoid path-to-regexp v8 breaking changes

Dockerfile

@@ -11,6 +11,6 @@ FROM node:20-alpine
 WORKDIR /app
 COPY --from=build /app/dist ./dist
 COPY server.js .
-RUN npm install express
+RUN npm install express@4
 EXPOSE 80
 CMD ["node", "server.js"]

server.js

@@ -54,7 +54,7 @@ app.post('/api/chat/stream', async (req, res) => {
 });
 
 // SPA fallback - all other routes serve index.html
-app.get('/*', (req, res) => {
+app.get('*', (req, res) => {
   res.sendFile(path.join(__dirname, 'dist', 'index.html'));
 });