Show a hint when Proxmox storage list comes back empty, not silently

Confirmed via the user's rebuild: my previous fix caught a *thrown*
storage-fetch error, but Proxmox's /nodes/{node}/storage instead
returns 200 with an empty array when the API token has no
Datastore.Audit on any storage — it filters the list per-token rather
than erroring the whole call. That shape has error === null and
storages.length === 0, so it fell through both my error banner and
the "no storages" render guard, showing nothing.

The Storage section now renders a hint (naming the missing
Datastore.Audit privilege) whenever storages is empty and no error
was recorded, instead of just disappearing. CPU/RAM/uptime are
unaffected by this since they come from the separate /status call.

Verified against a mock Proxmox API returning this exact 200-with-
empty-array shape for /storage.

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

web/src/pages/Proxmox.tsx

@@ -218,7 +218,7 @@ export default function Proxmox({ user }: { user: CurrentUser }) {
                           )}
                         </div>
 
-                        {n.storages.length > 0 && (
+                        {n.storages.length > 0 ? (
                           <div className="mt-3">
                             <div className="text-secondary small mb-1">Storage</div>
                             <table className="table table-sm table-vcenter mb-0">
@@ -239,6 +239,14 @@ export default function Proxmox({ user }: { user: CurrentUser }) {
                               </tbody>
                             </table>
                           </div>
+                        ) : (
+                          !n.error && (
+                            <div className="text-secondary small mt-3">
+                              No storage visible to this API token. Proxmox filters the storage list per-token —
+                              grant it <code>Datastore.Audit</code> (e.g. on <code>/storage</code>) to see disk
+                              usage here.
+                            </div>
+                          )
                         )}
                       </div>
                     </div>