Dashboard: per-host disk usage (0.21.0)

The per-host resource bar gained a Disk stat (used / total). The agent now
reports disk_total/disk_used via shutil.disk_usage on its stacks dir (a host
bind-mount), alongside the existing cpu/mem/containers fields; the local host
uses the existing system info disk data.

- agent_app.py: _disk_info() + disk_total/disk_used in _system_info().
- Frontend: ResourceBar gained diskUsed/diskTotal (5-column grid); AgentSystem
  type gained disk_total/disk_used.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

frontend/src/pages/Dashboard.tsx

@@ -11,6 +11,7 @@ import {
   Play,
   Square,
   RotateCw,
+  Server,
 } from "lucide-react";
 import { toast } from "sonner";
 import { Card, Spinner, StatusDot, Badge } from "@/components/ui";
@@ -62,6 +63,8 @@ export function Dashboard() {
           cpuCores={info.data?.cpu_cores ?? 0}
           memUsed={info.data?.ram.used ?? 0}
           memTotal={info.data?.ram.total ?? 0}
+          diskUsed={info.data?.disk.used ?? 0}
+          diskTotal={info.data?.disk.total ?? 0}
           containersRunning={info.data?.containers_running ?? 0}
           containersTotal={info.data?.containers_total ?? 0}
           dockerVersion={info.data?.docker_version ?? ""}
@@ -168,6 +171,8 @@ function AgentDashboardSection({ agent, isAdmin }: { agent: Agent; isAdmin: bool
           cpuCores={sys.data?.cpu_cores ?? 0}
           memUsed={sys.data?.mem_used ?? 0}
           memTotal={sys.data?.mem_total ?? 0}
+          diskUsed={sys.data?.disk_used ?? 0}
+          diskTotal={sys.data?.disk_total ?? 0}
           containersRunning={sys.data?.containers_running ?? 0}
           containersTotal={sys.data?.containers_total ?? 0}
           dockerVersion={sys.data?.docker_version ?? ""}
@@ -420,6 +425,8 @@ function ResourceBar({
   cpuCores,
   memUsed,
   memTotal,
+  diskUsed,
+  diskTotal,
   containersRunning,
   containersTotal,
   dockerVersion,
@@ -427,24 +434,31 @@ function ResourceBar({
   cpuCores: number;
   memUsed: number;
   memTotal: number;
+  diskUsed: number;
+  diskTotal: number;
   containersRunning: number;
   containersTotal: number;
   dockerVersion: string;
 }) {
   return (
-    <div className="mb-4 grid grid-cols-2 gap-4 md:grid-cols-4">
+    <div className="mb-4 grid grid-cols-2 gap-4 md:grid-cols-3 lg:grid-cols-5">
       <Stat icon={<Cpu className="h-5 w-5" />} label="CPU cores" value={cpuCores || "—"} />
       <Stat
         icon={<MemoryStick className="h-5 w-5" />}
         label="Memory"
         value={memTotal ? `${formatBytes(memUsed)} / ${formatBytes(memTotal)}` : "—"}
       />
+      <Stat
+        icon={<HardDrive className="h-5 w-5" />}
+        label="Disk"
+        value={diskTotal ? `${formatBytes(diskUsed)} / ${formatBytes(diskTotal)}` : "—"}
+      />
       <Stat
         icon={<Container className="h-5 w-5" />}
         label="Containers"
         value={`${containersRunning} / ${containersTotal}`}
       />
-      <Stat icon={<HardDrive className="h-5 w-5" />} label="Docker" value={dockerVersion || "—"} />
+      <Stat icon={<Server className="h-5 w-5" />} label="Docker" value={dockerVersion || "—"} />
     </div>
   );
 }