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/components/StatTile.js

@@ -0,0 +1,14 @@
+import { jsx as _jsx, jsxs as _jsxs } from "react/jsx-runtime";
+export function StatTile({ label, value, hint, color = 'idle' }) {
+    const ring = {
+        ok: 'ring-emerald-500/40',
+        warn: 'ring-amber-500/40',
+        err: 'ring-red-500/40',
+        idle: 'ring-slate-700',
+    }[color];
+    return (_jsxs("div", { className: [
+            'rounded-lg border border-slate-800 bg-slate-900/60 p-4',
+            'ring-1',
+            ring,
+        ].join(' '), children: [_jsx("div", { className: "text-xs uppercase tracking-wider text-slate-500", children: label }), _jsx("div", { className: "mt-1 text-2xl font-semibold text-slate-100 font-mono", children: value }), hint && _jsx("div", { className: "mt-1 text-xs text-slate-500", children: hint })] }));
+}