♻️ refactor(web): migrate React modules from .js to .jsx and align entrypoint

- Rename React components/pages/utilities that contain JSX to `.jsx` across `web/src`
- Update import paths and re-exports to match new `.jsx` extensions
- Fix Vite entry by switching `web/index.html` from `/src/index.js` to `/src/index.jsx`
- Verified remaining `.js` files are plain JS (hooks/helpers/constants) and do not require JSX
- No runtime behavior changes; extension and reference alignment only

Context: Resolves the Vite pre-transform error caused by the stale `/src/index.js` entry after migrating to `.jsx`.

web/src/components/layout/HeaderBar/ThemeToggle.jsx

@@ -0,0 +1,37 @@
+/*
+Copyright (C) 2025 QuantumNous
+
+This program is free software: you can redistribute it and/or modify
+it under the terms of the GNU Affero General Public License as
+published by the Free Software Foundation, either version 3 of the
+License, or (at your option) any later version.
+
+This program is distributed in the hope that it will be useful,
+but WITHOUT ANY WARRANTY; without even the implied warranty of
+MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+GNU Affero General Public License for more details.
+
+You should have received a copy of the GNU Affero General Public License
+along with this program. If not, see <https://www.gnu.org/licenses/>.
+
+For commercial licensing, please contact support@quantumnous.com
+*/
+
+import React from 'react';
+import { Button } from '@douyinfe/semi-ui';
+import { IconSun, IconMoon } from '@douyinfe/semi-icons';
+
+const ThemeToggle = ({ theme, onThemeToggle, t }) => {
+  return (
+    <Button
+      icon={theme === 'dark' ? <IconSun size="large" className="text-yellow-500" /> : <IconMoon size="large" className="text-gray-300" />}
+      aria-label={t('切换主题')}
+      onClick={onThemeToggle}
+      theme="borderless"
+      type="tertiary"
+      className="!p-1.5 !text-current focus:!bg-semi-color-fill-1 dark:focus:!bg-gray-700 !rounded-full !bg-semi-color-fill-0 dark:!bg-semi-color-fill-1 hover:!bg-semi-color-fill-1 dark:hover:!bg-semi-color-fill-2"
+    />
+  );
+};
+
+export default ThemeToggle;