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/branch-switcher.tsx

@@ -3,7 +3,7 @@ import { Pressable, View } from "react-native";
 import { useQueryClient } from "@tanstack/react-query";
 import { ChevronDown, GitBranch } from "lucide-react-native";
 import { StyleSheet, useUnistyles } from "react-native-unistyles";
-import { Combobox, ComboboxItem, type ComboboxOption } from "@/components/ui/combobox";
+import { Combobox, ComboboxItem } from "@/components/ui/combobox";
 import { useIsCompactFormFactor } from "@/constants/layout";
 import { useHostRuntimeClient, useHostRuntimeIsConnected } from "@/runtime/host-runtime";
 import { useToast } from "@/contexts/toast-context";