Dropdown async select component with server-side search.

Renders a search input and results dropdown where options are fetched from the server via search_fn callbacks on the FilterConfig.

Required Assigns

• filter - The Filter struct containing value and config
• myself - The parent LiveComponent's @myself for event targeting

Optional Assigns

• async_search_text - Map of filter_id => search string
• async_options - Map of filter_id => list of {value, label} tuples

Events (handled by parent)

• async_search - %{"id" => filter_id, "value" => search_text}
• async_select_option - %{"id" => filter_id, "value" => value, "label" => label}