Add desktop (Electron) and mobile (Expo) showcase apps

New workspace packages for demonstrating design system components:
- Desktop: Electron + Vite app with brand/theme switching
- Mobile: Expo React Native app with brand switching

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

packages/showcase/mobile/metro.config.js

@@ -0,0 +1,27 @@
+const { getDefaultConfig } = require('expo/metro-config');
+const path = require('path');
+
+const projectRoot = __dirname;
+const monorepoRoot = path.resolve(projectRoot, '..', '..', '..');
+
+const config = getDefaultConfig(projectRoot);
+
+// Watch the monorepo root for live changes to sibling packages
+config.watchFolders = [monorepoRoot];
+
+// Resolve node_modules from both the project and monorepo root (hoisted)
+config.resolver.nodeModulesPaths = [
+  path.resolve(projectRoot, 'node_modules'),
+  path.resolve(monorepoRoot, 'node_modules'),
+];
+
+// Block sibling packages' node_modules to prevent duplicate native modules
+const packagesDir = path.join(monorepoRoot, 'packages');
+const escapedPath = packagesDir.replace(/[/\\]/g, '[/\\\\]');
+config.resolver.blockList = [
+  new RegExp(
+    `^${escapedPath}[/\\\\](?!showcase[/\\\\]mobile)[^/\\\\]+[/\\\\]node_modules[/\\\\].*$`
+  ),
+];
+
+module.exports = config;