feat: add UPC to ASIN mapping and large file UPC analysis

Introduces the capability to resolve UPCs to ASINs using the Keepa API. This includes a new `upc-file` command for processing large Excel files of UPCs, a `upc` CLI tool for quick lookups, and API endpoints for web-based integration. The analysis pipeline was refactored into a reusable module to support both standard ASIN leads and new UPC-driven workflows.

src/types.ts

@@ -44,6 +44,23 @@ export interface KeepaData {
   categoryTree: string[];
 }
 
+export type KeepaUpcLookupStatus =
+  | "found"
+  | "invalid_upc"
+  | "not_found"
+  | "multiple_asins"
+  | "request_failed";
+
+export interface KeepaUpcLookupDetail {
+  requestedUpc: string;
+  normalizedUpc: string;
+  status: KeepaUpcLookupStatus;
+  asin: string | null;
+  candidateAsins: string[];
+  keepaData: KeepaData | null;
+  reason?: string;
+}
+
 export type SellabilityInfo = {
   canSell: boolean | null;
   sellabilityStatus: "available" | "restricted" | "not_available" | "unknown";