nodes: store and show host disk free; warn when low (node-26#41)

Checkin now carries disk_free_bytes/disk_total_bytes. Stored on the node doc
(not overwritten by older nodes that don't send them). Node page shows a Disk
row; node cards warn amber under 15% free, red under 5% or 2 GB. A full disk
stopped node-002 recording for 17 days while it showed Online.

Frontend unverified locally (no Node, #207); CI build typechecks.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

drb-frontend/app/nodes/[id]/page.tsx

@@ -16,6 +16,7 @@ import { MachineOutputNotice } from "@/components/ui/MachineOutputNotice";
 import { useAuth } from "@/components/AuthProvider";
 import { c2api } from "@/lib/c2api";
 import { errorMessage } from "@/lib/c2error";
+import { diskState, DISK_TEXT_CLASS } from "@/lib/nodeDisk";
 import type { NodeRecord } from "@/lib/types";
 
 function ApprovalBadge({ status }: { status: string | null }) {
@@ -218,6 +219,17 @@ export default function NodeDetailPage() {
             <span className="text-ink">{value}</span>
           </div>
         ))}
+        {(() => {
+          const disk = diskState(node);
+          return (
+            <div className="flex justify-between px-4 py-2.5">
+              <span className="text-ink-muted">Disk</span>
+              <span className={disk ? DISK_TEXT_CLASS[disk.level] : "text-ink-muted"}>
+                {disk ? `${disk.level !== "ok" ? "⚠ " : ""}${disk.label}` : "not reported (node software too old)"}
+              </span>
+            </div>
+          );
+        })()}
         <div className="flex justify-between px-4 py-2.5">
           <span className="text-ink-muted">Approval</span>
           <ApprovalBadge status={node.approval_status ?? null} />