frontend: scaffold Vite + React 19 + TS + Tailwind v4 + TanStack Query

Bare-minimum SPA that wires up to the FastAPI backend:

- Vite 6 + React 19 + TS strict, alias @/* to src/*
- Tailwind v4 via @tailwindcss/vite (no postcss)
- TanStack Query v5 with sane defaults (30s staleTime, no auto-refetch)
- React Router 7 for routing
- ECharts + Recharts available (charts land in Phase 1a)
- Vitest + @testing-library/react for tests
- Dev proxy /api → http://localhost:8080 (FastAPI)

Pages:
- Dashboard — pulls /networth, shows total + per-account cards.
  No chart yet (Phase 1a). Empty/error states for "no data" cases
  point users to the ingest CLI.

Header shows live API health (queue depth from /healthz). 274 KB JS
gzipped to 87 KB. typecheck + build pass.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

frontend/src/App.tsx

@@ -0,0 +1,36 @@
+import { useQuery } from '@tanstack/react-query';
+import { Route, Routes, Link } from 'react-router-dom';
+
+import { api } from '@/api/client';
+import { Dashboard } from '@/pages/Dashboard';
+
+export function App() {
+  const health = useQuery({ queryKey: ['health'], queryFn: api.health });
+
+  return (
+    <div className="min-h-screen flex flex-col">
+      <header className="border-b border-slate-200 bg-white">
+        <div className="max-w-7xl mx-auto px-6 py-4 flex items-center justify-between">
+          <Link to="/" className="text-xl font-semibold tracking-tight">
+            fire-planner
+          </Link>
+          <div className="text-xs text-slate-500">
+            api:{' '}
+            <span className={health.data ? 'text-emerald-600' : 'text-amber-600'}>
+              {health.isLoading
+                ? '…'
+                : health.data
+                  ? `ok (queue=${health.data.queue_depth})`
+                  : 'unreachable'}
+            </span>
+          </div>
+        </div>
+      </header>
+      <main className="flex-1 max-w-7xl w-full mx-auto px-6 py-8">
+        <Routes>
+          <Route path="/" element={<Dashboard />} />
+        </Routes>
+      </main>
+    </div>
+  );
+}