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/.gitignore

@@ -0,0 +1,16 @@
+node_modules
+dist
+.npm
+*.tsbuildinfo
+.env.local
+.env.*.local
+*.log
+.vscode/*
+!.vscode/extensions.json
+.idea
+.DS_Store
+*.suo
+*.ntvs*
+*.njsproj
+*.sln
+*.sw?