feat: US-001 — scaffold NeuralDesk Electron + React app

- electron-forge 7 + Vite plugin (vite-typescript template)
- React 19 + TypeScript 5 strict mode
- TanStack Router with file-based routing (4 routes: /, /timeline, /tasks, /projects)
- Tailwind CSS 3 + PostCSS with Figma design tokens (sidebar, primary, muted)
- Framer Motion, Lucide React, shadcn/ui utilities (cn, CVA, clsx, twMerge)
- AppShell layout: 240px sidebar with collapse toggle, active route highlighting
- Vite configs use .mts extension to avoid ESM/CJS conflict with electron-forge
- Full package build verified (linux x64)

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/renderer/index.tsx

@@ -0,0 +1,14 @@
+import { StrictMode } from 'react';
+import { createRoot } from 'react-dom/client';
+import { RouterProvider } from '@tanstack/react-router';
+import { router } from './router';
+import './globals.css';
+
+const rootElement = document.getElementById('root');
+if (!rootElement) throw new Error('Root element not found');
+
+createRoot(rootElement).render(
+  <StrictMode>
+    <RouterProvider router={router} />
+  </StrictMode>,
+);