feat(admin): add search with submit and safe-area layout

Add submit-based search to admin books page and switch borrows
search from debounced to submit-based for consistency. Update
layout headers and nav bars to respect mobile safe-area insets
via CSS custom properties.

src/features/borrows/hooks.ts

@@ -1,5 +1,5 @@
 import { useQuery, useMutation, useQueryClient } from "@tanstack/react-query"
-import { getAllMyBorrows, returnBookForMe } from "@/api/borrows"
+import { getAllMyBorrows, searchMyBorrows, returnBookForMe } from "@/api/borrows"
 import { toast } from "sonner"
 import { getErrorMessage } from "@/lib/errors"
 
@@ -10,6 +10,14 @@ export function useMyBorrows() {
   })
 }
 
+export function useSearchMyBorrows(query: string) {
+  return useQuery({
+    queryKey: ["myBorrows", "search", query],
+    queryFn: () => searchMyBorrows(query),
+    enabled: query.length > 0,
+  })
+}
+
 export function useReturnBook() {
   const qc = useQueryClient()
   return useMutation({