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/components/layout/AppShell.tsx

@@ -0,0 +1,113 @@
+import { useState } from 'react';
+import { Link, useRouterState } from '@tanstack/react-router';
+import {
+  House,
+  ChartGantt,
+  ClipboardCheck,
+  FolderKanban,
+  PanelLeft,
+} from 'lucide-react';
+import { cn } from '@/lib/utils';
+
+const NAV_ITEMS = [
+  { to: '/', icon: House, label: 'Home' },
+  { to: '/timeline', icon: ChartGantt, label: 'Timeline' },
+  { to: '/tasks', icon: ClipboardCheck, label: 'Tasks' },
+  { to: '/projects', icon: FolderKanban, label: 'Projects' },
+] as const;
+
+interface AppShellProps {
+  children: React.ReactNode;
+}
+
+export function AppShell({ children }: AppShellProps) {
+  const [collapsed, setCollapsed] = useState(false);
+  const routerState = useRouterState();
+  const currentPath = routerState.location.pathname;
+
+  return (
+    <div className="flex h-screen w-screen overflow-hidden bg-background">
+      {/* Sidebar */}
+      <aside
+        className={cn(
+          'flex flex-col h-full bg-sidebar border-r border-sidebar-border transition-all duration-200 overflow-hidden shrink-0',
+          collapsed ? 'w-16' : 'w-60',
+        )}
+      >
+        {/* Logo */}
+        <div
+          className={cn(
+            'flex items-center gap-3 px-3 py-3 shrink-0',
+            collapsed && 'justify-center',
+          )}
+        >
+          <div className="size-7 rounded-lg bg-primary flex items-center justify-center shrink-0">
+            <svg
+              width="16"
+              height="16"
+              viewBox="0 0 24 24"
+              fill="none"
+              className="text-primary-foreground"
+            >
+              <path
+                d="M12 2L13.5 8.5L20 10L13.5 11.5L12 18L10.5 11.5L4 10L10.5 8.5L12 2Z"
+                fill="currentColor"
+              />
+            </svg>
+          </div>
+          {!collapsed && (
+            <span className="font-semibold text-sm text-foreground">
+              NeuralDesk
+            </span>
+          )}
+        </div>
+
+        {/* Nav */}
+        <nav className="flex flex-col gap-0.5 px-2 flex-1 mt-2">
+          {NAV_ITEMS.map(({ to, icon: Icon, label }) => {
+            const isActive =
+              to === '/'
+                ? currentPath === '/'
+                : currentPath.startsWith(to);
+
+            return (
+              <Link
+                key={to}
+                to={to}
+                className={cn(
+                  'flex items-center gap-2 h-8 px-3 rounded-md text-sm text-sidebar-foreground transition-colors',
+                  'hover:bg-sidebar-accent',
+                  isActive && 'bg-sidebar-accent font-medium',
+                )}
+              >
+                <Icon size={16} className="shrink-0" />
+                {!collapsed && <span className="truncate">{label}</span>}
+              </Link>
+            );
+          })}
+        </nav>
+
+        {/* Collapse toggle */}
+        <div className="px-2 pb-3 shrink-0">
+          <button
+            onClick={() => setCollapsed((c) => !c)}
+            className={cn(
+              'flex items-center gap-2 h-8 px-3 rounded-md text-sm text-sidebar-foreground w-full',
+              'hover:bg-sidebar-accent transition-colors',
+              collapsed && 'justify-center',
+            )}
+            title={collapsed ? 'Expand sidebar' : 'Collapse sidebar'}
+          >
+            <PanelLeft size={16} className="shrink-0" />
+            {!collapsed && <span>Collapse</span>}
+          </button>
+        </div>
+      </aside>
+
+      {/* Main content */}
+      <main className="flex-1 min-w-0 overflow-hidden relative">
+        {children}
+      </main>
+    </div>
+  );
+}