feat(09-01): add SvelteKit module mocks for browser tests

- Mock $app/navigation (goto, invalidate, invalidateAll, beforeNavigate, afterNavigate)
- Mock $app/stores (page, navigating, updated)
- Mock $app/environment (browser, dev, building)
- Add Vitest browser type references

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

vitest-setup-client.ts

@@ -0,0 +1,36 @@
+/// <reference types="@vitest/browser/matchers" />
+/// <reference types="@vitest/browser/providers/playwright" />
+
+import { vi } from 'vitest';
+import { writable } from 'svelte/store';
+
+// Mock $app/navigation
+vi.mock('$app/navigation', () => ({
+	goto: vi.fn(() => Promise.resolve()),
+	invalidate: vi.fn(() => Promise.resolve()),
+	invalidateAll: vi.fn(() => Promise.resolve()),
+	beforeNavigate: vi.fn(),
+	afterNavigate: vi.fn()
+}));
+
+// Mock $app/stores
+vi.mock('$app/stores', () => ({
+	page: writable({
+		url: new URL('http://localhost'),
+		params: {},
+		route: { id: null },
+		status: 200,
+		error: null,
+		data: {},
+		form: null
+	}),
+	navigating: writable(null),
+	updated: { check: vi.fn(), subscribe: writable(false).subscribe }
+}));
+
+// Mock $app/environment
+vi.mock('$app/environment', () => ({
+	browser: true,
+	dev: true,
+	building: false
+}));