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>

frontend/src/App.jsx

@@ -3,20 +3,25 @@ import {
   AppBar, Toolbar, Typography, Container, Box, Paper,
   TextField, Button, List, ListItem, ListItemText,
   CircularProgress, Chip, Grid, Card, CardContent,
-  Tabs, Tab, Divider, IconButton
+  Tabs, Tab, Divider, IconButton, Select, MenuItem,
+  FormControl, InputLabel
 } from '@mui/material';
 import {
   Send as SendIcon,
   Search as SearchIcon,
   Description as DocIcon,
   Support as SupportIcon,
-  CloudUpload as UploadIcon
+  CloudUpload as UploadIcon,
+  Language as LanguageIcon
 } from '@mui/icons-material';
 import axios from 'axios';
 import io from 'socket.io-client';
+import ReactMarkdown from 'react-markdown';
+import remarkGfm from 'remark-gfm';
 
-const API_URL = import.meta.env.VITE_API_URL || 'http://localhost:8000';
-const CHAT_URL = import.meta.env.VITE_CHAT_URL || 'http://localhost:8001';
+// Use relative URLs to work with nginx proxy in production
+const API_URL = import.meta.env.VITE_API_URL || (typeof window !== 'undefined' ? window.location.origin + '/api' : 'http://localhost:8000');
+const CHAT_URL = import.meta.env.VITE_CHAT_URL || (typeof window !== 'undefined' ? window.location.origin : 'http://localhost:8001');
 
 function App() {
   const [activeTab, setActiveTab] = useState(0);
@@ -56,6 +61,7 @@ function ChatInterface() {
   const [input, setInput] = useState('');
   const [loading, setLoading] = useState(false);
   const [socket, setSocket] = useState(null);
+  const [language, setLanguage] = useState('en');
   const messagesEndRef = useRef(null);
   
   useEffect(() => {
@@ -90,8 +96,8 @@ function ChatInterface() {
     
     setMessages(prev => [...prev, userMessage]);
     setLoading(true);
-    
-    socket.emit('chat', { message: input, history: messages });
+
+    socket.emit('chat', { message: input, history: messages, language: language });
     setInput('');
   };
   
@@ -99,11 +105,32 @@ function ChatInterface() {
     <Grid container spacing={3}>
       <Grid item xs={12} md={8}>
         <Paper sx={{ height: '70vh', display: 'flex', flexDirection: 'column' }}>
-          <Box sx={{ p: 2, bgcolor: 'primary.main', color: 'white' }}>
-            <Typography variant="h6">Technical Support Chat</Typography>
-            <Typography variant="caption">
-              AI-powered assistant with access to datacenter documentation
-            </Typography>
+          <Box sx={{ p: 2, bgcolor: 'primary.main', color: 'white', display: 'flex', justifyContent: 'space-between', alignItems: 'center' }}>
+            <Box>
+              <Typography variant="h6">Technical Support Chat</Typography>
+              <Typography variant="caption">
+                AI-powered assistant with access to datacenter documentation
+              </Typography>
+            </Box>
+            <FormControl size="small" sx={{ minWidth: 120, bgcolor: 'white', borderRadius: 1 }}>
+              <InputLabel id="language-select-label">Language</InputLabel>
+              <Select
+                labelId="language-select-label"
+                value={language}
+                label="Language"
+                onChange={(e) => setLanguage(e.target.value)}
+                startAdornment={<LanguageIcon sx={{ mr: 0.5, color: 'action.active' }} />}
+              >
+                <MenuItem value="en">🇬🇧 English</MenuItem>
+                <MenuItem value="it">🇮🇹 Italiano</MenuItem>
+                <MenuItem value="es">🇪🇸 Español</MenuItem>
+                <MenuItem value="fr">🇫🇷 Français</MenuItem>
+                <MenuItem value="de">🇩🇪 Deutsch</MenuItem>
+                <MenuItem value="pt">🇵🇹 Português</MenuItem>
+                <MenuItem value="zh">🇨🇳 中文</MenuItem>
+                <MenuItem value="ja">🇯🇵 日本語</MenuItem>
+              </Select>
+            </FormControl>
           </Box>
           
           <Box sx={{ flexGrow: 1, overflow: 'auto', p: 2 }}>
@@ -117,7 +144,38 @@ function ChatInterface() {
                     maxWidth: '70%',
                     bgcolor: msg.role === 'user' ? 'primary.light' : 'grey.100'
                   }}>
-                    <Typography variant="body1">{msg.content}</Typography>
+                    {msg.role === 'user' ? (
+                      <Typography variant="body1">{msg.content}</Typography>
+                    ) : (
+                      <Box sx={{
+                        '& h1, & h2, & h3': { mt: 2, mb: 1 },
+                        '& h1': { fontSize: '1.5rem', fontWeight: 600 },
+                        '& h2': { fontSize: '1.3rem', fontWeight: 600 },
+                        '& h3': { fontSize: '1.1rem', fontWeight: 600 },
+                        '& p': { mb: 1 },
+                        '& ul, & ol': { pl: 2, mb: 1 },
+                        '& li': { mb: 0.5 },
+                        '& code': {
+                          bgcolor: 'rgba(0,0,0,0.05)',
+                          p: 0.5,
+                          borderRadius: 1,
+                          fontFamily: 'monospace',
+                          fontSize: '0.9em'
+                        },
+                        '& pre': {
+                          bgcolor: 'rgba(0,0,0,0.05)',
+                          p: 2,
+                          borderRadius: 1,
+                          overflow: 'auto',
+                          '& code': { bgcolor: 'transparent', p: 0 }
+                        },
+                        '& hr': { my: 2, border: 'none', borderTop: '1px solid rgba(0,0,0,0.12)' }
+                      }}>
+                        <ReactMarkdown remarkPlugins={[remarkGfm]}>
+                          {msg.content}
+                        </ReactMarkdown>
+                      </Box>
+                    )}
                     {msg.related_docs && (
                       <Box sx={{ mt: 1 }}>
                         {msg.related_docs.map((doc, i) => (