Implements collapsed select rendering, dropdown overlay with optgroup/disabled support,
click interaction (open/close/select), form submission, and Escape-to-close. Code review
fixed: layout invalidation on selection change, select_states threading through fast paths,
Escape key handling, form reset for selects, and added integration tests.
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
71f263f298