feat(vpn): intégration Tailscale/Headscale + URLs publiques par sous-domaine

- Ajout d'un conteneur Tailscale côté serveur pour joindre les agents via IPs Tailscale
- Configuration Headscale exposé en HTTPS via Caddy (headscale.alfrednobel.edudeploy.com)
- Caddy configuré pour les sous-domaines avec TLS on-demand
- Middleware et route proxy Next.js pour router les sous-domaines vers les agents
- Ajout du champ domain sur Establishment et affichage de l'URL publique dans le dashboard
- Agent Windows v0.2.3 avec proxy Tailscale par instance pour contourner Docker Desktop
- Templates WordPress/PrestaShop bindés sur 0.0.0.0 pour être accessibles via Tailscale

server/app/dashboard/instances/page.tsx

@@ -21,10 +21,18 @@ export default async function InstancesPage() {
     where: establishmentId
       ? { node: { student: { class: { establishmentId } } } }
       : {},
-    include: { node: { include: { student: { include: { class: true } } } }, template: true },
+    include: { node: { include: { student: { include: { class: { include: { establishment: true } } } } } }, template: true },
     orderBy: { createdAt: "desc" },
   });
 
+  const enrichedInstances = instances.map((inst) => {
+    const domain = inst.node.student?.class.establishment?.domain;
+    return {
+      ...inst,
+      publicUrl: domain ? `https://${inst.id}.${domain}` : null,
+    };
+  });
+
   return (
     <div className="space-y-6">
       <div className="flex items-center justify-between">
@@ -44,11 +52,12 @@ export default async function InstancesPage() {
                 <TableHead>Étudiant</TableHead>
                 <TableHead>Port</TableHead>
                 <TableHead>Statut</TableHead>
+                <TableHead>URL publique</TableHead>
                 <TableHead>Actions</TableHead>
               </TableRow>
             </TableHeader>
             <TableBody>
-              {instances.map((inst) => (
+              {enrichedInstances.map((inst: any) => (
                 <TableRow key={inst.id}>
                   <TableCell className="font-medium">{inst.id.slice(0, 8)}...</TableCell>
                   <TableCell>{inst.template.name}</TableCell>
@@ -58,6 +67,9 @@ export default async function InstancesPage() {
                   <TableCell>
                     <Badge variant={inst.status === "running" ? "success" : inst.status === "error" ? "destructive" : "secondary"}>{inst.status}</Badge>
                   </TableCell>
+                  <TableCell>
+                    {inst.publicUrl ? <a href={inst.publicUrl} target="_blank" rel="noopener" className="text-blue-600 hover:underline">{inst.publicUrl}</a> : "-"}
+                  </TableCell>
                   <TableCell>
                     <InstanceActions instanceId={inst.id} status={inst.status} />
                   </TableCell>
@@ -65,7 +77,7 @@ export default async function InstancesPage() {
               ))}
               {instances.length === 0 && (
                 <TableRow>
-                  <TableCell colSpan={7} className="text-center text-muted-foreground">Aucune instance</TableCell>
+                  <TableCell colSpan={8} className="text-center text-muted-foreground">Aucune instance</TableCell>
                 </TableRow>
               )}
             </TableBody>