feat: add left/right cluster handles on Proxmox group node

frontend/src/components/canvas/nodes/ProxmoxGroupNode.tsx

@@ -76,6 +76,40 @@ export function ProxmoxGroupNode(props: NodeProps<Node<NodeData>>) {
 
       <Handle type="target" position={Position.Top} className="!bg-[#30363d] !border-[#8b949e]" />
       <Handle type="source" position={Position.Bottom} className="!bg-[#30363d] !border-[#8b949e]" />
+
+      {/* Cluster handles — left/right for same-cluster links */}
+      <Handle
+        type="source"
+        position={Position.Left}
+        id="cluster-left-src"
+        title="Same cluster"
+        className="!w-2.5 !h-2.5 !rounded-sm"
+        style={{ background: '#ff6e00', borderColor: '#ff6e0088', top: 20 }}
+      />
+      <Handle
+        type="target"
+        position={Position.Left}
+        id="cluster-left-tgt"
+        title="Same cluster"
+        className="!w-2.5 !h-2.5 !rounded-sm"
+        style={{ background: '#ff6e00', borderColor: '#ff6e0088', top: 36 }}
+      />
+      <Handle
+        type="source"
+        position={Position.Right}
+        id="cluster-right-src"
+        title="Same cluster"
+        className="!w-2.5 !h-2.5 !rounded-sm"
+        style={{ background: '#ff6e00', borderColor: '#ff6e0088', top: 20 }}
+      />
+      <Handle
+        type="target"
+        position={Position.Right}
+        id="cluster-right-tgt"
+        title="Same cluster"
+        className="!w-2.5 !h-2.5 !rounded-sm"
+        style={{ background: '#ff6e00', borderColor: '#ff6e0088', top: 36 }}
+      />
     </>
   )
 }