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/message-input.tsx

@@ -2,13 +2,11 @@ import {
   View,
   Text,
   TextInput,
-  Pressable,
   ActivityIndicator,
   NativeSyntheticEvent,
   TextInputContentSizeChangeEventData,
   TextInputKeyPressEventData,
   TextInputSelectionChangeEventData,
-  BackHandler,
 } from "react-native";
 import {
   useState,