refactor: reorganize directory structure into src/

Move all source code directories into src/ for cleaner project structure:
- pages/, components/, utils/, config/, providers/, types/, lib/, assets/, entrypoints/ → src/
- Use WXT srcDir config to resolve @/ alias to src/
- Update tsconfig, vitest, eslint, tailwind configs
- Remove scattered README.md files from subdirectories
- Update documentation (AGENTS.md, CODING_STANDARDS.md, README.md)
- Fix pre-existing lint error in RouterProvider.tsx

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

src/components/__tests__/TopBar.test.tsx

@@ -0,0 +1,90 @@
+import { beforeEach, describe, expect, it, vi } from 'vitest';
+import { fireEvent, render, screen } from '@testing-library/react';
+import type { PageType } from '@/types/storage';
+import React from 'react';
+import TopBar from '@/components/TopBar';
+import { RouterProvider } from '@/providers/RouterProvider';
+import { ThemeModeProvider } from '@/providers/ThemeModeProvider';
+
+// matchMedia must be mocked before ThemeModeProvider is imported
+Object.defineProperty(window, 'matchMedia', {
+  writable: true,
+  value: vi.fn().mockImplementation((query: string) => ({
+    matches: false,
+    media: query,
+    onchange: null,
+    addListener: vi.fn(),
+    removeListener: vi.fn(),
+    addEventListener: vi.fn(),
+    removeEventListener: vi.fn(),
+    dispatchEvent: vi.fn(),
+  })),
+});
+
+const mockRouterValue = {
+  currentPage: 'dashboard' as PageType,
+  visiblePages: ['dashboard', 'timestamp'] as PageType[],
+  pageOrder: ['timestamp'] as PageType[],
+  isLoaded: true,
+  navigateTo: vi.fn(),
+  syncNavigation: vi.fn(),
+  goBack: vi.fn(),
+  setVisiblePages: vi.fn(),
+  setPageOrder: vi.fn(),
+};
+
+vi.mock('@/providers/RouterProvider', () => ({
+  useRouter: () => mockRouterValue,
+  RouterProvider: ({ children }: { children: React.ReactNode }) => children,
+}));
+
+describe('TopBar 组件', () => {
+  beforeEach(() => {
+    vi.clearAllMocks();
+  });
+
+  const renderWithProvider = (ui: React.ReactElement) => {
+    return render(
+      <ThemeModeProvider>
+        <RouterProvider>{ui}</RouterProvider>
+      </ThemeModeProvider>,
+    );
+  };
+
+  describe('渲染测试', () => {
+    it('不在 dashboard 时应渲染返回按钮', () => {
+      mockRouterValue.currentPage = 'timestamp';
+      renderWithProvider(<TopBar onOpenOptions={vi.fn()} />);
+      expect(screen.getByLabelText('返回')).toBeInTheDocument();
+    });
+
+    it('在 dashboard 上不应渲染返回按钮', () => {
+      mockRouterValue.currentPage = 'dashboard';
+      renderWithProvider(<TopBar onOpenOptions={vi.fn()} />);
+      expect(screen.queryByLabelText('返回')).not.toBeInTheDocument();
+    });
+
+    it('应渲染设置按钮', () => {
+      renderWithProvider(<TopBar onOpenOptions={vi.fn()} />);
+      expect(screen.getByLabelText('设置')).toBeInTheDocument();
+    });
+  });
+
+  describe('交互测试', () => {
+    it('点击设置按钮时应调用 onOpenOptions', () => {
+      const handleOpenOptions = vi.fn();
+      renderWithProvider(<TopBar onOpenOptions={handleOpenOptions} />);
+
+      fireEvent.click(screen.getByLabelText('设置'));
+      expect(handleOpenOptions).toHaveBeenCalledTimes(1);
+    });
+
+    it('点击返回按钮时应调用 goBack', () => {
+      mockRouterValue.currentPage = 'timestamp';
+      renderWithProvider(<TopBar onOpenOptions={vi.fn()} />);
+
+      fireEvent.click(screen.getByLabelText('返回'));
+      expect(mockRouterValue.goBack).toHaveBeenCalledTimes(1);
+    });
+  });
+});