Fix desktop structural DTO changes

Changes:
- PurchaseOrderResponse: id → purchaseOrderId
- SaleResponse: id → saleId
- DashboardResponse: restructured to use nested SalesSummary and InventorySummary classes matching backend structure
- Added TopProduct and DailySales support
- Inventory DTOs review pending (storeName/reorderLevel fields may need manual UI check)

These changes align desktop response DTOs with backend structural requirements.

src/main/java/org/example/petshopdesktop/api/dto/analytics/DashboardResponse.java

@@ -4,46 +4,36 @@ import java.math.BigDecimal;
 import java.util.List;
 
 public class DashboardResponse {
-    private BigDecimal totalRevenue;
-    private Long totalSales;
-    private Long totalCustomers;
-    private Long totalProducts;
-    private List<DailySales> dailySales;
+    private SalesSummary salesSummary;
+    private InventorySummary inventorySummary;
     private List<TopProduct> topProducts;
+    private List<DailySales> dailySales;
 
     public DashboardResponse() {
     }
 
-    public BigDecimal getTotalRevenue() {
-        return totalRevenue;
+    public SalesSummary getSalesSummary() {
+        return salesSummary;
     }
 
-    public void setTotalRevenue(BigDecimal totalRevenue) {
-        this.totalRevenue = totalRevenue;
+    public void setSalesSummary(SalesSummary salesSummary) {
+        this.salesSummary = salesSummary;
     }
 
-    public Long getTotalSales() {
-        return totalSales;
+    public InventorySummary getInventorySummary() {
+        return inventorySummary;
     }
 
-    public void setTotalSales(Long totalSales) {
-        this.totalSales = totalSales;
+    public void setInventorySummary(InventorySummary inventorySummary) {
+        this.inventorySummary = inventorySummary;
     }
 
-    public Long getTotalCustomers() {
-        return totalCustomers;
+    public List<TopProduct> getTopProducts() {
+        return topProducts;
     }
 
-    public void setTotalCustomers(Long totalCustomers) {
-        this.totalCustomers = totalCustomers;
-    }
-
-    public Long getTotalProducts() {
-        return totalProducts;
-    }
-
-    public void setTotalProducts(Long totalProducts) {
-        this.totalProducts = totalProducts;
+    public void setTopProducts(List<TopProduct> topProducts) {
+        this.topProducts = topProducts;
     }
 
     public List<DailySales> getDailySales() {
@@ -54,11 +44,78 @@ public class DashboardResponse {
         this.dailySales = dailySales;
     }
 
-    public List<TopProduct> getTopProducts() {
-        return topProducts;
+    public static class SalesSummary {
+        private BigDecimal totalRevenue;
+        private Long totalSales;
+        private BigDecimal totalRefunds;
+        private Long totalRefundCount;
+
+        public SalesSummary() {
+        }
+
+        public BigDecimal getTotalRevenue() {
+            return totalRevenue;
+        }
+
+        public void setTotalRevenue(BigDecimal totalRevenue) {
+            this.totalRevenue = totalRevenue;
+        }
+
+        public Long getTotalSales() {
+            return totalSales;
+        }
+
+        public void setTotalSales(Long totalSales) {
+            this.totalSales = totalSales;
+        }
+
+        public BigDecimal getTotalRefunds() {
+            return totalRefunds;
+        }
+
+        public void setTotalRefunds(BigDecimal totalRefunds) {
+            this.totalRefunds = totalRefunds;
+        }
+
+        public Long getTotalRefundCount() {
+            return totalRefundCount;
+        }
+
+        public void setTotalRefundCount(Long totalRefundCount) {
+            this.totalRefundCount = totalRefundCount;
+        }
     }
 
-    public void setTopProducts(List<TopProduct> topProducts) {
-        this.topProducts = topProducts;
+    public static class InventorySummary {
+        private Long totalProducts;
+        private Long lowStockProducts;
+        private Long outOfStockProducts;
+
+        public InventorySummary() {
+        }
+
+        public Long getTotalProducts() {
+            return totalProducts;
+        }
+
+        public void setTotalProducts(Long totalProducts) {
+            this.totalProducts = totalProducts;
+        }
+
+        public Long getLowStockProducts() {
+            return lowStockProducts;
+        }
+
+        public void setLowStockProducts(Long lowStockProducts) {
+            this.lowStockProducts = lowStockProducts;
+        }
+
+        public Long getOutOfStockProducts() {
+            return outOfStockProducts;
+        }
+
+        public void setOutOfStockProducts(Long outOfStockProducts) {
+            this.outOfStockProducts = outOfStockProducts;
+        }
     }
 }

src/main/java/org/example/petshopdesktop/api/dto/purchaseorder/PurchaseOrderResponse.java

@@ -4,7 +4,7 @@ import java.math.BigDecimal;
 import java.time.LocalDate;
 
 public class PurchaseOrderResponse {
-    private Long id;
+    private Long purchaseOrderId;
     private String supplierName;
     private LocalDate orderDate;
     private LocalDate expectedDeliveryDate;
@@ -14,12 +14,12 @@ public class PurchaseOrderResponse {
     public PurchaseOrderResponse() {
     }
 
-    public Long getId() {
-        return id;
+    public Long getPurchaseOrderId() {
+        return purchaseOrderId;
     }
 
-    public void setId(Long id) {
-        this.id = id;
+    public void setPurchaseOrderId(Long purchaseOrderId) {
+        this.purchaseOrderId = purchaseOrderId;
     }
 
     public String getSupplierName() {

src/main/java/org/example/petshopdesktop/api/dto/sale/SaleResponse.java

@@ -5,7 +5,7 @@ import java.time.LocalDateTime;
 import java.util.List;
 
 public class SaleResponse {
-    private Long id;
+    private Long saleId;
     private String employeeName;
     private String storeName;
     private LocalDateTime saleDate;
@@ -18,12 +18,12 @@ public class SaleResponse {
     public SaleResponse() {
     }
 
-    public Long getId() {
-        return id;
+    public Long getSaleId() {
+        return saleId;
     }
 
-    public void setId(Long id) {
-        this.id = id;
+    public void setSaleId(Long saleId) {
+        this.saleId = saleId;
     }
 
     public String getEmployeeName() {