Add client-side validation to ensure a repository is selected before
form submission. Split owner/repo on both change and submit events.
Show inline error messages via form-error div. Update CreateIssue
handler to return HTMX-friendly HTML error fragments on 400/500.
Closesleeworks-agents/gitea-mobile#30
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>