feat: add multilingual chat support with markdown rendering

- Fix Socket.IO proxy configuration in nginx for chat connectivity
- Add Socket.IO path routing (/socket.io/) with WebSocket upgrade support
- Fix frontend healthcheck to use curl instead of wget
- Add react-markdown and remark-gfm for proper markdown rendering
- Implement language selector in chat interface (8 languages supported)
- Add language parameter to chat agent and LLM prompts
- Support English, Italian, Spanish, French, German, Portuguese, Chinese, Japanese

This resolves the chat connection issues and enables users to receive
AI responses in their preferred language with properly formatted markdown.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

deploy/docker/Dockerfile.frontend

@@ -33,9 +33,9 @@ COPY deploy/docker/nginx.conf /etc/nginx/conf.d/default.conf
 # Expose port
 EXPOSE 80
 
-# Health check
+# Health check (use curl which is available in nginx:alpine)
 HEALTHCHECK --interval=30s --timeout=10s --start-period=5s --retries=3 \
-    CMD wget --no-verbose --tries=1 --spider http://localhost/health || exit 1
+    CMD curl -f http://127.0.0.1/health || exit 1
 
 # Run nginx
 CMD ["nginx", "-g", "daemon off;"]

deploy/docker/nginx.conf

@@ -36,7 +36,23 @@ server {
         proxy_set_header X-Forwarded-Proto $scheme;
     }
 
-    # WebSocket for chat
+    # Socket.IO for chat (Socket.IO uses /socket.io/ path by default)
+    location /socket.io/ {
+        proxy_pass http://chat:8001/socket.io/;
+        proxy_http_version 1.1;
+        proxy_set_header Upgrade $http_upgrade;
+        proxy_set_header Connection "upgrade";
+        proxy_set_header Host $host;
+        proxy_set_header X-Real-IP $remote_addr;
+        proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
+        proxy_set_header X-Forwarded-Proto $scheme;
+
+        # Socket.IO specific settings
+        proxy_buffering off;
+        proxy_read_timeout 86400;
+    }
+
+    # WebSocket for chat (alternative endpoint)
     location /ws/ {
         proxy_pass http://chat:8001/;
         proxy_http_version 1.1;