Add per-VM autostart checkbox (single-select, persisted)

Only one VM can be marked for autostart at a time — checking a new
one unchecks the previous. Matched by host+vmid since the same vmid
can exist on multiple standalone Proxmox hosts in a cluster setup.

src/renderer/styles.css

@@ -250,6 +250,20 @@ body.vms-page {
 
 .vm-info { flex: 1; min-width: 0; }
 
+.vm-autostart {
+  display: flex;
+  align-items: center;
+  gap: 0.35rem;
+  font-size: 0.75rem;
+  color: var(--muted);
+  cursor: pointer;
+  white-space: nowrap;
+  flex-shrink: 0;
+  user-select: none;
+}
+
+.vm-autostart input { cursor: pointer; }
+
 .vm-name {
   font-size: 0.97rem;
   font-weight: 600;