feat(header): add GitHub star button to top bar

Compact pill (GitHub icon | star count) placed left of the version
display. Star count is fetched from the GitHub API once per 24h and
cached in localStorage; the button hides entirely when no count is
available (e.g. air-gapped deployments), matching the existing update-
check graceful-degradation pattern. Fetch is bounded by a 4s abort
timeout to avoid hanging requests offline.

src/layouts/extraRender.tsx

@@ -18,6 +18,7 @@ import { useAtom } from 'jotai';
 import { useMemo } from 'react';
 import styled from 'styled-components';
 import { DEFAULT_ENTER_PAGE } from '../config/settings';
+import GithubStar from './github-star';
 
 const NewLabel = styled.span`
   position: relative;
@@ -260,6 +261,7 @@ export const ExtraContent = (props: { isDarkTheme?: boolean }) => {
     <Wrapper>
       {contextHolder}
       <PluginExtraField name="OrgSwitcher" isDarkTheme={isDarkTheme} />
+      {process.env.ENABLE_ENTERPRISE !== 'true' && <GithubStar />}
       <div
         style={{
           display: 'flex',