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/main.tsx

@@ -0,0 +1,29 @@
+import { StrictMode } from 'react';
+import { createRoot } from 'react-dom/client';
+import { QueryClient, QueryClientProvider } from '@tanstack/react-query';
+import { BrowserRouter } from 'react-router-dom';
+
+import './index.css';
+import { App } from '@/App';
+
+const queryClient = new QueryClient({
+  defaultOptions: {
+    queries: {
+      staleTime: 30_000,
+      refetchOnWindowFocus: false,
+    },
+  },
+});
+
+const root = document.getElementById('root');
+if (!root) throw new Error('#root element missing');
+
+createRoot(root).render(
+  <StrictMode>
+    <QueryClientProvider client={queryClient}>
+      <BrowserRouter>
+        <App />
+      </BrowserRouter>
+    </QueryClientProvider>
+  </StrictMode>,
+);