feat: Add UK inventory sync from Dropbox

- Create new API endpoint api/fetch-uk-inventory.ts
- Add processUKInventoryExcel function in dataProcessor.ts
- Update handleVendorStockFetch to load PANEU + UK in parallel
- Configure Vite proxy for UK inventory endpoint
- UK stock correctly populates 'uk' field in vendorStockMap

services/dataProcessor.ts

@@ -1985,6 +1985,89 @@ export const processVendorStockExcel = async (fileOrBuffer: File | ArrayBuffer):
     }
 };
 
+/**
+ * Process UK Inventory Excel file from Amazon Vendor Central.
+ * This file contains ONLY UK inventory, so all stock goes to the 'uk' property.
+ * It merges with an existing vendorStockMap to combine PANEU + UK data.
+ */
+export const processUKInventoryExcel = async (
+    fileOrBuffer: File | ArrayBuffer,
+    existingMap?: Map<string, { eu: number; uk: number }>
+): Promise<Map<string, { eu: number; uk: number }>> => {
+    try {
+        const arrayBuffer = fileOrBuffer instanceof File
+            ? await fileOrBuffer.arrayBuffer()
+            : fileOrBuffer;
+        const workbook = XLSX.read(arrayBuffer, { type: 'array' });
+        const sheetName = workbook.SheetNames[0];
+        const worksheet = workbook.Sheets[sheetName];
+        const jsonData: any[][] = XLSX.utils.sheet_to_json(worksheet, { header: 1 });
+
+        // Start with existing map or create new one
+        const vendorStockMap = existingMap || new Map<string, { eu: number; uk: number }>();
+
+        // Find header row (it contains "ASIN")
+        let headerRowIndex = -1;
+        for (let i = 0; i < Math.min(jsonData.length, 20); i++) {
+            if (jsonData[i] && (jsonData[i].includes('ASIN') || jsonData[i].includes('asin'))) {
+                headerRowIndex = i;
+                break;
+            }
+        }
+
+        if (headerRowIndex === -1) {
+            console.warn("[UK Inventory] Could not find header row");
+            return vendorStockMap;
+        }
+
+        const headers: any[] = jsonData[headerRowIndex];
+        const asinIdx = headers.findIndex(h => String(h || '').toUpperCase() === 'ASIN');
+
+        // Find "Sellable On Hand Units" column (same logic as PANEU)
+        let stockIdx = headers.findIndex(h => String(h || '').toUpperCase() === 'SELLABLE ON HAND UNITS');
+
+        if (stockIdx === -1) {
+            stockIdx = headers.findIndex(h => {
+                const sh = String(h || '').toUpperCase();
+                return sh.includes('SELLABLE') && sh.includes('UNITS') &&
+                    !sh.includes('UNSELLABLE') && !sh.includes('AGED');
+            });
+        }
+
+        // Fallback to default index if not found
+        const finalAsinIdx = asinIdx !== -1 ? asinIdx : 0;
+        const finalStockIdx = stockIdx !== -1 ? stockIdx : 14; // UK file has it at index 14
+
+        console.log(`[UK Inventory] ASIN Column: "${headers[finalAsinIdx]}" (Index: ${finalAsinIdx})`);
+        console.log(`[UK Inventory] Stock Column: "${headers[finalStockIdx]}" (Index: ${finalStockIdx})`);
+
+        let ukCount = 0;
+        for (let i = headerRowIndex + 1; i < jsonData.length; i++) {
+            const row = jsonData[i];
+            if (!row || row.length <= Math.max(finalAsinIdx, finalStockIdx)) continue;
+
+            const asin = String(row[finalAsinIdx] || '').trim().toUpperCase();
+            if (!asin) continue;
+
+            const stockValue = parseUnits(String(row[finalStockIdx] || '0'));
+
+            if (!vendorStockMap.has(asin)) {
+                vendorStockMap.set(asin, { eu: 0, uk: 0 });
+            }
+
+            const current = vendorStockMap.get(asin)!;
+            current.uk += stockValue;
+            ukCount++;
+        }
+
+        console.log(`[UK Inventory] Processed ${ukCount} UK stock entries`);
+        return vendorStockMap;
+    } catch (error) {
+        console.error("Error processing UK Inventory Excel:", error);
+        throw error;
+    }
+};
+
 export const calculateVelocityMap = (data: SalesRecord[]): Map<string, number> => {
     // 4-Week Average Sales Calculation
     const validYears = data.map(r => r.year).filter(y => y > 0);