dashboard-v2 PR 2: frontend SPA + serve integration

React 19 + Vite + Tailwind + wouter (tiny router, no external
state library). Consumes the /api/v2/* endpoints shipped in PR 1.
Serves under /v2/* so the legacy dashboard at / stays live.

Pages:
* CommandCenter (/)      — fleet strip + this-node stat tiles
* NodeDetail (/nodes/:name) — per-node deep dive
* StorageBrowser (/storage/{blobs,tags,refs,snapshots}) — tables
  with prefix filter
* RefTrackingPage (/refs/tracking) — grouped by repo

Backend changes:
* claw-store serve grows --v2-static-dir <path>
* build_app split into build_app_with_v2 for the extra static
  mount
* /v2/* falls through to index.html so wouter client routing works

New systemd unit: clawstor-dashboard.service. Points at both
static dirs; installs on any node.

dashboard/ (legacy) untouched. dashboard-v2/ built to
target/dashboard-v2/dist for deploy.

Deploy sequence per node:
1. cp target/release/claw-store  ~/clawstor-deploy/
2. rsync dashboard-v2/dist/      ~/clawstor-deploy/dashboard-v2/
3. cp deploy/systemd/clawstor-dashboard.service ~/.config/systemd/user/
4. systemctl --user daemon-reload && enable --now clawstor-dashboard.service

Cross-node fan-out for /api/v2/node/:name/status is PR 3.
Action POSTs (scrub/gc/snapshot/pin) are PR 4.

dashboard-v2/src/pages/CommandCenter.tsx

@@ -0,0 +1,114 @@
+import { useEffect, useState } from 'react';
+import { api, NodeStatusV2, fmtBytes } from '../lib/api';
+import { NodeCard } from '../components/NodeCard';
+import { StatTile } from '../components/StatTile';
+
+// Fleet-wide command center. Reads `/api/v2/node/local/status` from
+// this node. Cross-node fan-out is server-side once PR 3 lands;
+// until then we assume the operator hits any node's dashboard and
+// sees that node's storage state plus quick nav to the others.
+//
+// Poll cadence: 10 s. Cheap: 5 filesystem walks.
+export function CommandCenter() {
+  const [me, setMe] = useState<NodeStatusV2 | null>(null);
+  const [err, setErr] = useState<string | null>(null);
+  const [tick, setTick] = useState(0);
+
+  useEffect(() => {
+    api
+      .nodeStatus('local')
+      .then((n) => {
+        setMe(n);
+        setErr(null);
+      })
+      .catch((e) => setErr(String(e)));
+  }, [tick]);
+
+  useEffect(() => {
+    const id = setInterval(() => setTick((t) => t + 1), 10_000);
+    return () => clearInterval(id);
+  }, []);
+
+  return (
+    <div className="space-y-6">
+      <div>
+        <h1 className="text-2xl font-semibold text-slate-100">Fleet</h1>
+        <div className="text-sm text-slate-500">
+          this dashboard was served by{' '}
+          <span className="font-mono text-slate-300">
+            {me?.node_name ?? '…'}
+          </span>
+          {' · click any node card to drill in'}
+        </div>
+      </div>
+
+      {err && (
+        <div className="rounded border border-red-800 bg-red-950/40 p-3 text-red-300 text-sm">
+          {err}
+        </div>
+      )}
+
+      <section className="grid grid-cols-1 sm:grid-cols-2 lg:grid-cols-3 gap-4">
+        {me && (
+          <NodeCard
+            node={me}
+            loading={false}
+            error={null}
+          />
+        )}
+        {['tank', 'architect', 'morpheus']
+          .filter((n) => n !== me?.node_name)
+          .map((n) => (
+            <NodeCard
+              key={n}
+              node={{
+                node_name: n,
+                blob_store_root: null,
+                blob_count: 0,
+                tag_count: 0,
+                ref_count: 0,
+                snapshot_count: 0,
+                ref_tracking_count: 0,
+                blob_store_bytes: 0,
+              }}
+              loading
+              error={null}
+            />
+          ))}
+      </section>
+
+      {me && (
+        <section>
+          <h2 className="text-lg font-semibold text-slate-100 mb-3">
+            This node
+          </h2>
+          <div className="grid grid-cols-2 sm:grid-cols-3 lg:grid-cols-6 gap-3">
+            <StatTile label="blobs" value={me.blob_count.toLocaleString()} color="ok" />
+            <StatTile
+              label="tags"
+              value={me.tag_count}
+              color={me.tag_count > 0 ? 'ok' : 'idle'}
+            />
+            <StatTile
+              label="refs"
+              value={me.ref_count}
+              color={me.ref_count > 0 ? 'ok' : 'idle'}
+            />
+            <StatTile label="snapshots" value={me.snapshot_count} color="ok" />
+            <StatTile
+              label="ref-tracking"
+              value={me.ref_tracking_count}
+              color={me.ref_tracking_count > 0 ? 'ok' : 'idle'}
+            />
+            <StatTile
+              label="store size"
+              value={fmtBytes(me.blob_store_bytes)}
+              hint={me.blob_store_root ?? undefined}
+              color="ok"
+            />
+          </div>
+        </section>
+      )}
+    </div>
+  );
+}