Remove sticky top-0 from chapter drawer header

iOS Safari fails to paint sticky descendants of overflow-hidden ancestors
until a repaint is triggered, causing the "Chapters / N total" header to
render invisibly. The sticky was unnecessary — the header sits outside
the drawer's scroll container, so it never actually needed to stick.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

components/PageReader.tsx

@@ -675,7 +675,7 @@ export function PageReader({
             className="absolute bottom-0 left-0 right-0 max-h-[75vh] bg-background rounded-t-3xl shadow-2xl overflow-hidden"
             onClick={(e) => e.stopPropagation()}
           >
-            <div className="sticky top-0 bg-background z-10 border-b border-border">
+            <div className="bg-background border-b border-border">
               <div className="flex justify-center pt-2.5 pb-1.5">
                 <div className="w-10 h-1 rounded-full bg-muted/40" />
               </div>