fix(store): replace ZStack overlay sticky approach with native pinnedViews + reliable scroll tracking

- Use LazyVStack(pinnedViews: [.sectionHeaders]) for native section header stickiness
- Move ScrollOffsetReader outside LazyVStack (sibling) to prevent lazy-unload breaking scroll tracking
- Add baseline capture to ScrollOffsetReader to correctly normalize offset regardless of ScrollView content insets
- Apply safeAreaTop padding to categoryTabs only when pinned (isCategoryTabsPinned), preventing oversized header before scroll
- Remove complex ZStack dual-tabs overlay, stickyProgress logic, and categoryTabsStickyProgress
- categoryTabs now accepts isPinned flag with easeInOut(0.15s) animation on pin transition

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

pedi-foods/Sources/PediFoods/Views/Main/StoreDetailSupport.swift

@@ -22,6 +22,7 @@ struct ScrollOffsetPreferenceKey: PreferenceKey {
 
 struct ScrollOffsetReader: View {
     @Binding var offsetY: CGFloat
+    @State private var baseline: CGFloat? = nil
 
     var body: some View {
         Color.clear
@@ -35,9 +36,10 @@ struct ScrollOffsetReader: View {
                 }
             )
             .onPreferenceChange(ScrollOffsetPreferenceKey.self) { minY in
-                let normalizedOffset = max(0, -minY)
-                if abs(offsetY - normalizedOffset) > 0.5 {
-                    offsetY = normalizedOffset
+                if baseline == nil { baseline = minY }
+                let offset = max(0, (baseline ?? 0) - minY)
+                if abs(offsetY - offset) > 0.5 {
+                    offsetY = offset
                 }
             }
     }