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/hooks/use-keyboard-action-handler.ts

@@ -3,7 +3,6 @@ import { useEffect } from "react";
 import {
   keyboardActionDispatcher,
   type KeyboardActionDefinition,
-  type KeyboardActionHandler,
   type KeyboardActionId,
 } from "@/keyboard/keyboard-action-dispatcher";