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/index.css

@@ -140,11 +140,14 @@ html.mobile body {
 }
 
 html.no-select * {
+  -webkit-user-select: none !important;
   user-select: none !important;
 }
 
 html.no-select input,
 html.no-select textarea,
 html.no-select [data-selectable] {
+  -webkit-user-select: text !important;
   user-select: text !important;
-}
+}
+