The HTML <datalist> approach for tag autocomplete was unreliable across
browsers — showed empty suggestions or no dropdown at all.
Replace with a custom Alpine.js dropdown:
- New tag-dropdown.ts shared module: searchTagSuggestions() queries
/api/media-items/search?tags=...&library_id=... and returns results
- Bookshelf: absolute-positioned dropdown below tags_filter input, shows
tag name + book count per suggestion
- Keyboard navigation: ArrowUp/Down to highlight, Enter to select,
Escape to close
- Click suggestion to populate the filter input