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/routes/timeline.tsx

@@ -0,0 +1,13 @@
+import { createFileRoute } from '@tanstack/react-router';
+
+export const Route = createFileRoute('/timeline')({
+  component: TimelinePage,
+});
+
+function TimelinePage() {
+  return (
+    <div className="flex items-center justify-center h-full text-muted-foreground text-sm">
+      Timeline — coming in US-008
+    </div>
+  );
+}