feat(core): initialize project skeleton with Electron + React + TypeScript

Set up the complete project foundation for ClawX, a graphical AI assistant:

- Electron main process with IPC handlers, menu, tray, and gateway management
- React renderer with routing, layout components, and page scaffolding
- Zustand state management for gateway, settings, channels, skills, chat, and cron
- shadcn/ui components with Tailwind CSS and CSS variable theming
- Build tooling with Vite, electron-builder, and TypeScript configuration
- Testing setup with Vitest and Playwright
- Development configurations (ESLint, Prettier, gitignore, env example)

src/components/common/LoadingSpinner.tsx

@@ -0,0 +1,36 @@
+/**
+ * Loading Spinner Component
+ * Displays a spinning loader animation
+ */
+import { Loader2 } from 'lucide-react';
+import { cn } from '@/lib/utils';
+
+interface LoadingSpinnerProps {
+  size?: 'sm' | 'md' | 'lg';
+  className?: string;
+}
+
+const sizeClasses = {
+  sm: 'h-4 w-4',
+  md: 'h-8 w-8',
+  lg: 'h-12 w-12',
+};
+
+export function LoadingSpinner({ size = 'md', className }: LoadingSpinnerProps) {
+  return (
+    <div className={cn('flex items-center justify-center', className)}>
+      <Loader2 className={cn('animate-spin text-primary', sizeClasses[size])} />
+    </div>
+  );
+}
+
+/**
+ * Full page loading spinner
+ */
+export function PageLoader() {
+  return (
+    <div className="flex h-full items-center justify-center">
+      <LoadingSpinner size="lg" />
+    </div>
+  );
+}