feat: ebay splashui challenge solver

argon2id pow → /challengesvc/answer → chlgref cookie
warm homepage for akamai cookies, detect 307 redirect,
solve + retry transparently in fetchEbayItems flow

packages/core/test/ebay-core.test.ts

@@ -47,17 +47,22 @@ describe("eBay Scraper Cookie Handling", () => {
   test("should ignore request cookie overrides and rely on EBAY_COOKIE", async () => {
     await fetchEbayItems("laptop", 1000);
 
-    expect(global.fetch).toHaveBeenCalledTimes(1);
+    // First call is homepage warm-up, second is search
+    expect(global.fetch).toHaveBeenCalledTimes(2);
 
-    const firstFetchCall = (global.fetch as unknown as ReturnType<typeof mock>)
-      .mock.calls[0];
-    if (!firstFetchCall) {
-      throw new Error("Expected fetch to be called");
+    // The search request is the second call
+    const secondFetchCall = (global.fetch as unknown as ReturnType<typeof mock>)
+      .mock.calls[1];
+    if (!secondFetchCall) {
+      throw new Error("Expected search fetch to be called");
     }
 
-    const [, init] = firstFetchCall;
+    const [searchUrl, init] = secondFetchCall;
     const headers = (init as RequestInit).headers as Record<string, string>;
 
+    expect(searchUrl).toBe(
+      "https://www.ebay.ca/sch/i.html?_nkw=laptop&_sacat=0&_from=R40&LH_BIN=1&LH_PrefLoc=1",
+    );
     expect(headers.Cookie).toBeUndefined();
   });