Fix login UX issues
- Hide login button on homepage (avoid duplicate login UI)
- Add actor-typeahead to login modal for handle autocompletion
- Add z-index: 1000 to actor-typeahead for proper layering
- Add onchange handler to modal input for typeahead sync
Fixes:
- No more confusing dual login UI on homepage
- Modal now has same typeahead functionality as main form
- Typeahead dropdown renders above all page content
Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>