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/StoreDetailView+Components.swift

@@ -195,10 +195,15 @@ extension StoreDetailView {
         }
     }
 
-    func categoryTabs(proxy: ScrollViewProxy, topExtension: CGFloat = 0, stickyProgress: CGFloat = 0) -> some View {
-        let chipPaddingH: CGFloat = 10 + 6 * stickyProgress
-        let chipPaddingV: CGFloat = 4 + 5 * stickyProgress
-        let containerPaddingV: CGFloat = 2 + 8 * stickyProgress
+    func categoryTabs(proxy: ScrollViewProxy, isPinned: Bool = false) -> some View {
+        let safeTop: CGFloat = {
+            guard isPinned else { return 0 }
+            #if canImport(UIKit)
+            return UIDevice.appSafeAreaTop
+            #else
+            return 0
+            #endif
+        }()
 
         return ScrollView(.horizontal, showsIndicators: false) {
             HStack(spacing: 10) {
@@ -217,8 +222,8 @@ extension StoreDetailView {
                         Text(category.name)
                             .font(AppTypography.heading3)
                             .foregroundStyle(active ? AppColors.textInverse : AppColors.textMuted)
-                            .padding(.horizontal, chipPaddingH)
-                            .padding(.vertical, chipPaddingV)
+                            .padding(.horizontal, 16)
+                            .padding(.vertical, 9)
                             .background(active ? AppColors.primary : AppColors.surface)
                             .clipShape(Capsule())
                     }
@@ -226,16 +231,11 @@ extension StoreDetailView {
                 }
             }
             .padding(.horizontal, 16)
-            .padding(.vertical, containerPaddingV)
+            .padding(.vertical, 10)
         }
+        .padding(.top, safeTop)
         .background(AppColors.backgroundLight)
-        .overlay(alignment: .top) {
-            AppColors.backgroundLight
-                .frame(height: topExtension)
-                .frame(maxWidth: .infinity)
-                .offset(y: -topExtension)
-                .allowsHitTesting(false)
-        }
+        .animation(.easeInOut(duration: 0.15), value: isPinned)
     }
 
     func productCard(_ item: StoreCatalogListItem, in category: StoreCatalogCategory) -> some View {