[lcenavigationview-adoption] Adopt LCENavigationView across 15 screens

Standardizes the back button to a single shared component
(AppBackButtonIcon, 32x32/14pt) instead of ~16 hand-duplicated
52x52/24pt copies, and wires each screen through LCENavigationView
per this project's mandatory-usage rule. Home and Store Detail
intentionally excluded - both have bespoke header designs (collapsing
header, hero-image overlay) this change would visually disrupt.

PediFoods/Components/AppBackButtonIcon.swift

@@ -0,0 +1,13 @@
+import SwiftUI
+
+struct AppBackButtonIcon: View {
+    var body: some View {
+        Image(systemName: "chevron.left")
+            .font(.system(size: 14, weight: .semibold))
+            .foregroundStyle(AppColors.textPrimary)
+            .frame(width: 32, height: 32)
+            .background(AppColors.surface)
+            .clipShape(Circle())
+            .shadow(color: .black.opacity(0.06), radius: 8, y: 2)
+    }
+}