fix: page indicator not tracking scroll when showing all pages

The IntersectionObserver was only set up when virtualizing pages,
but the page indicator needs to work in both modes:
- Virtualized mode (worksheet creator): lazy load pages
- Non-virtualized mode (shared worksheets): show all pages

Changed observer setup to always run when totalPages > 1, regardless
of virtualization mode. The visible pages update logic still only
runs when virtualizing to avoid unnecessary state updates.

This fixes the page indicator being stuck on page 1 when initialData
is provided (non-virtualized mode).

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

apps/web/src/app/create/worksheets/components/WorksheetPreview.tsx

@@ -161,18 +161,13 @@ function PreviewContent({ formState, initialData, isScrolling = false }: Workshe
     }
   })
 
-  // Intersection Observer to track visible pages (only when virtualizing)
+  // Intersection Observer to track current page (works with or without virtualization)
   useEffect(() => {
     console.log('[PAGE INDICATOR] Observer useEffect triggered - shouldVirtualize:', shouldVirtualize, 'totalPages:', totalPages, 'refsReady:', refsReady)
 
-    if (!shouldVirtualize) {
-      console.log('[PAGE INDICATOR] Skipping observer setup - not virtualizing')
-      return // Skip virtualization when showing all pages
-    }
-
     if (totalPages <= 1) {
       console.log('[PAGE INDICATOR] Skipping observer setup - only', totalPages, 'page(s)')
-      return // No need for virtualization with single page
+      return // No need for page tracking with single page
     }
 
     // Wait for refs to be populated
@@ -211,7 +206,8 @@ function PreviewContent({ formState, initialData, isScrolling = false }: Workshe
           console.log('[PAGE INDICATOR] No visible page (maxRatio = 0), keeping current page')
         }
 
-        // Update visible pages set
+        // Update visible pages set (only when virtualizing)
+        if (shouldVirtualize) {
           setVisiblePages((prev) => {
             const next = new Set(prev)
 
@@ -229,6 +225,7 @@ function PreviewContent({ formState, initialData, isScrolling = false }: Workshe
 
             return next
           })
+        }
       },
       {
         root: null, // Use viewport as root (scrolling happens in parent)