Replace the OptionsFunc-based MultiSelectWithSearch with a custom huh
Field implementation. huh's OptionsFunc runs in a goroutine, causing
data races with selection state and stale cache issues that made
selections disappear on toggle or search changes.
The custom field (multiSelectSearchField) combines a text input and
multi-select list in a single field with full control over the update
loop. Search runs asynchronously via tea.Cmd when the user presses
Enter, with a themed spinner during loading. Selections are stored in
a simple map — no goroutine races, no Eval cache, no syncAccessor.
Also adds defensive validation for mismatched Keys/Labels slices from
searchFunc.
Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
