Add batch processing for product price retrieval: Implement getProductPricesInCitiesBatch method in FalukantService for handling multiple product price requests in a single API call. Update FalukantController and router to support new endpoint, and refactor RevenueSection and SaleSection components to utilize batch processing for improved performance and reduced API calls.

frontend/src/components/falukant/SaleSection.vue

@@ -293,27 +293,26 @@
         }
       },
       async loadPricesForInventory() {
-        const requests = this.inventory.map(async (item) => {
-          const itemKey = `${item.region.id}-${item.product.id}-${item.quality}`;
-          if (this.loadingPrices.has(itemKey)) return;
-          this.loadingPrices.add(itemKey);
-          try {
-            const currentPrice = item.product.sellCost || 0;
-            const { data } = await apiClient.get('/api/falukant/products/prices-in-cities', {
-              params: {
-                productId: item.product.id,
-                currentPrice: currentPrice
-              }
-            });
-            item.betterPrices = data || [];
-          } catch (error) {
-            console.error(`Error loading prices for item ${itemKey}:`, error);
-            item.betterPrices = [];
-          } finally {
-            this.loadingPrices.delete(itemKey);
+        if (this.inventory.length === 0) return;
+        const currentRegionId = this.inventory[0]?.region?.id ?? null;
+        const items = this.inventory.map(item => ({
+          productId: item.product.id,
+          currentPrice: item.product.sellCost || 0
+        }));
+        try {
+          const { data } = await apiClient.post('/api/falukant/products/prices-in-cities-batch', {
+            currentRegionId,
+            items
+          });
+          for (const item of this.inventory) {
+            item.betterPrices = data && data[item.product.id] ? data[item.product.id] : [];
           }
-        });
-        await Promise.all(requests);
+        } catch (error) {
+          console.error('Error loading prices for inventory:', error);
+          for (const item of this.inventory) {
+            item.betterPrices = [];
+          }
+        }
       },
       getCityPriceClass(branchType) {
         if (branchType === 'store') return 'city-price-green';