feat(nav): add MobileTabBar with active state and safe-area padding

Fixed vitest resolve conditions to use browser entry for Svelte 5.

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

frontend/vite.config.ts

@@ -0,0 +1,16 @@
+import { sveltekit } from '@sveltejs/kit/vite';
+import { defineConfig } from 'vitest/config';
+import tailwindcss from '@tailwindcss/vite';
+
+export default defineConfig({
+	plugins: [tailwindcss(), sveltekit()],
+	test: {
+		include: ['src/**/*.{test,spec}.{js,ts}'],
+		globals: true,
+		environment: 'jsdom',
+		setupFiles: ['src/test-setup.ts']
+	},
+	resolve: {
+		conditions: ['browser']
+	}
+});