Add drag-and-drop section reordering

src/hooks/useCarts.ts

@@ -158,6 +158,18 @@ export function useCarts() {
     }))
   }
 
+  function reorderSections(fromId: string, toId: string) {
+    mutateActiveCart(cart => {
+      const sections = [...cart.sections]
+      const fromIdx = sections.findIndex(s => s.id === fromId)
+      const toIdx   = sections.findIndex(s => s.id === toId)
+      if (fromIdx === -1 || toIdx === -1 || fromIdx === toIdx) return cart
+      const [moved] = sections.splice(fromIdx, 1)
+      sections.splice(toIdx, 0, moved)
+      return { ...cart, sections }
+    })
+  }
+
   // ── Item management ───────────────────────────────────────────────────────
 
   function addItem(sectionId: string, item: Product | Drone) {
@@ -220,6 +232,7 @@ export function useCarts() {
     addSection,
     removeSection,
     renameSection,
+    reorderSections,
     addItem,
     updateItem,
     removeItem,