chore: apply oxlint fix-suggestions (unused imports + useless fragments)

Scoped to only `no-unused-vars` and `react/jsx-no-useless-fragment` —
the safe subset of --fix-suggestions. Primary changes:

- Remove unused named imports from statements
- Remove unused default/type imports entirely
- Collapse `<><Single/></>` fragments to `<Single/>`

Verified clean: typecheck + format + lint all green.

packages/app/src/components/combined-model-selector.tsx

@@ -18,7 +18,6 @@ const IS_WEB = platformIsWeb;
 
 import { Combobox, ComboboxItem } from "@/components/ui/combobox";
 import { getProviderIcon } from "@/components/provider-icons";
-import type { FavoriteModelRow } from "@/hooks/use-form-preferences";
 import {
   buildModelRows,
   buildSelectedTriggerLabel,