Make Proxmox node cards full-width to match the VM/LXC table

Node cards were col-lg-6 (half width, side by side), while the
VM/LXC table below is full width -- looked mismatched, especially
with a single node. Full width also gives the left/right system-
info/storage split inside each card more room to breathe.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

web/src/pages/Proxmox.tsx

@@ -166,7 +166,7 @@ export default function Proxmox({ user }: { user: CurrentUser }) {
               {nodeStatsError && <div className="alert alert-danger">{nodeStatsError}</div>}
               <div className="row row-cards mb-3">
                 {nodeStats?.map((n) => (
-                  <div className="col-lg-6" key={n.node}>
+                  <div className="col-12" key={n.node}>
                     <div className="card h-100">
                       <div className="card-header">
                         <h3 className="card-title">