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/locales/en-US/common.ts

@@ -169,6 +169,7 @@ export default {
   'common.time.hour': 'hour',
   'common.time.minute': 'minutes',
   'common.issue.report': 'Report an issue',
+  'common.github.star.tooltip': 'Star us on GitHub',
   'common.social.discord': 'Join Our Discord',
   'common.table.mark': 'Comment',
   'common.table.rollback.mark': 'Rollback Comment',