Add isTokenError() helper that detects HTTP 401/403 responses from the
Gitea API, and redirectOnTokenError() that redirects to /settings with
an error=token_expired query parameter. Update Dashboard, ListIssues,
and ListPulls handlers to check for token errors. The settings page now
displays an error banner explaining the token needs to be refreshed.
Closesleeworks-agents/gitea-mobile#192
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>