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/books/hooks.ts

@@ -1,5 +1,5 @@
 import { useQuery, useMutation, useQueryClient } from "@tanstack/react-query"
-import { getAllBooks } from "@/api/books"
+import { getAllBooks, searchBook } from "@/api/books"
 import { borrowBookForMe } from "@/api/borrows"
 import { toast } from "sonner"
 import { getErrorMessage } from "@/lib/errors"
@@ -12,6 +12,14 @@ export function useBooks() {
   })
 }
 
+export function useSearchBooks(query: string) {
+  return useQuery({
+    queryKey: ["books", "search", query],
+    queryFn: () => searchBook(query),
+    enabled: query.length > 0,
+  })
+}
+
 export function useBorrowBook() {
   const qc = useQueryClient()
   return useMutation({