Add authentication system with next-auth (CredentialsProvider + JWT)

- Login page with email/password
- Auth middleware (proxy) protecting all routes
- Seed endpoint for admin user creation (admin@optiquestock.com / admin123)
- Session provider wrapping root layout
- User info + logout button in header
- Updated POS sales route to track authenticated user

src/app/page.tsx

@@ -1,6 +1,8 @@
 'use client'
 
 import { useState } from 'react'
+import { useSession, signOut } from 'next-auth/react'
+import { useRouter } from 'next/navigation'
 import { Card, CardContent, CardDescription, CardHeader, CardTitle } from '@/components/ui/card'
 import { Button } from '@/components/ui/button'
 import { Badge } from '@/components/ui/badge'
@@ -13,7 +15,9 @@ import {
   BarChart3,
   Eye,
   LayoutDashboard,
-  Wrench
+  Wrench,
+  LogOut,
+  User
 } from 'lucide-react'
 import POSModule from '@/components/pos/POSModule'
 import { ProduitListe } from '@/components/products/ProduitListe'
@@ -90,8 +94,15 @@ const modules: ModuleCard[] = [
 ]
 
 export default function Home() {
+  const { data: session } = useSession()
+  const router = useRouter()
   const [currentModule, setCurrentModule] = useState<Module>('HOME')
 
+  if (!session) {
+    router.push('/login')
+    return null
+  }
+
   const renderModule = () => {
     if (currentModule === 'HOME') {
       return (
@@ -347,9 +358,18 @@ export default function Home() {
               <Badge variant="outline" className="text-sm">
                 v1.0.0
               </Badge>
-              <div className="h-8 w-8 rounded-full bg-primary flex items-center justify-center text-primary-foreground text-sm font-medium">
-                OP
+              <div className="flex items-center gap-2 text-sm text-gray-600">
+                <User className="h-4 w-4" />
+                <span className="hidden sm:inline">{session?.user?.name}</span>
               </div>
+              <Button
+                variant="ghost"
+                size="icon"
+                onClick={() => signOut({ callbackUrl: '/login' })}
+                title="Se déconnecter"
+              >
+                <LogOut className="h-4 w-4" />
+              </Button>
             </div>
           </div>
         </div>