refactor: 移除 Dashboard 页面及相关功能，更新路由和组件逻辑

- 移除 Dashboard 相关的组件、特性和测试代码，简化项目结构。
- 更新 PageSkeleton 组件，默认渲染工具页面骨架。
- 修改 RouterContainer 和 RouterProvider 以适应新的默认路由策略，确保用户直接访问 timestamp 页面。
- 更新测试用例，确保在新结构下的功能正常。

src/layout/FeatureNav/__tests__/index.test.tsx

@@ -0,0 +1,54 @@
+import { beforeEach, describe, expect, it, vi } from 'vitest';
+import { fireEvent, render, screen } from '@testing-library/react';
+import type { PageType } from '@/types/storage';
+import FeatureNav from '@/layout/FeatureNav';
+
+const mockNavigateTo = vi.fn();
+
+const mockRouterValue = {
+  currentPage: 'timestamp' as PageType,
+  visiblePages: ['timestamp', 'jwt', 'storageCleaner'] as PageType[],
+  pageOrder: ['jwt', 'timestamp', 'storageCleaner'] as PageType[],
+  recentlyUsedTools: [] as PageType[],
+  isLoaded: true,
+  navigateTo: mockNavigateTo,
+  setVisiblePages: vi.fn(),
+  setPageOrder: vi.fn(),
+};
+
+vi.mock('@/providers/RouterProvider', () => ({
+  useRouter: () => mockRouterValue,
+}));
+
+describe('FeatureNav 组件', () => {
+  beforeEach(() => {
+    vi.clearAllMocks();
+    mockRouterValue.currentPage = 'timestamp';
+    mockRouterValue.pageOrder = ['jwt', 'timestamp', 'storageCleaner'];
+    mockRouterValue.visiblePages = ['timestamp', 'jwt', 'storageCleaner'];
+  });
+
+  it('应渲染全部可见工具图标', () => {
+    render(<FeatureNav />);
+
+    expect(screen.getByLabelText('JWT 解析')).toBeInTheDocument();
+    expect(screen.getByLabelText('时间戳')).toBeInTheDocument();
+    expect(screen.getByLabelText('存储清理')).toBeInTheDocument();
+  });
+
+  it('点击图标应调用 navigateTo', () => {
+    render(<FeatureNav />);
+
+    fireEvent.click(screen.getByLabelText('JWT 解析'));
+    expect(mockNavigateTo).toHaveBeenCalledWith('jwt');
+  });
+
+  it('当前页对应项应有 active 样式与 aria-current', () => {
+    render(<FeatureNav />);
+
+    const activeButton = screen.getByLabelText('时间戳');
+    expect(activeButton).toHaveAttribute('aria-current', 'page');
+    expect(activeButton).toHaveClass('bg-muted');
+    expect(activeButton).toHaveClass('border-primary');
+  });
+});