fix: remove backend health check to prevent 404 errors

- Remove unnecessary backend connectivity check in Layout component
- Simplify Layout component by removing unused imports and state
- Application now works seamlessly in demo mode without backend errors
- Clean console output without 404 errors on startup

src/components/Layout.tsx

@@ -1,8 +1,7 @@
 import React from 'react'
-import { AppBar, Toolbar, Typography, Container, Box, Alert, Snackbar } from '@mui/material'
+import { AppBar, Toolbar, Typography, Container, Box } from '@mui/material'
 import { useNavigate, useLocation } from 'react-router-dom'
 import { NavigationTabs } from './NavigationTabs'
-import { useState, useEffect } from 'react'
 
 interface LayoutProps {
   children: React.ReactNode
@@ -11,26 +10,6 @@ interface LayoutProps {
 export const Layout: React.FC<LayoutProps> = ({ children }) => {
   const navigate = useNavigate()
   const location = useLocation()
-  const [showDemoAlert, setShowDemoAlert] = useState(false)
-
-  useEffect(() => {
-    // Vérifier si le backend est accessible
-    const checkBackend = async () => {
-      try {
-        const response = await fetch('http://localhost:8000/health', { 
-          method: 'GET',
-          signal: AbortSignal.timeout(2000)
-        })
-        if (!response.ok) {
-          setShowDemoAlert(true)
-        }
-      } catch (error) {
-        setShowDemoAlert(true)
-      }
-    }
-    
-    checkBackend()
-  }, [])
 
   return (
     <Box sx={{ flexGrow: 1 }}>
@@ -52,21 +31,6 @@ export const Layout: React.FC<LayoutProps> = ({ children }) => {
       <Container maxWidth="xl" sx={{ mt: 3, mb: 3 }}>
         {children}
       </Container>
-
-      <Snackbar
-        open={showDemoAlert}
-        autoHideDuration={6000}
-        onClose={() => setShowDemoAlert(false)}
-        anchorOrigin={{ vertical: 'bottom', horizontal: 'center' }}
-      >
-        <Alert 
-          onClose={() => setShowDemoAlert(false)} 
-          severity="info" 
-          sx={{ width: '100%' }}
-        >
-          Mode démonstration activé - Backend non accessible
-        </Alert>
-      </Snackbar>
     </Box>
   )
 }