fix(tests): target window.URL instead of URL for createObjectURL mocking

In jsdom, source modules resolve bare 'URL' identifiers through
window.URL (the jsdom window object), not through globalThis.URL (Node's
URL class). On GitHub Actions these are distinct objects, so all prior
attempts (Object.defineProperty, direct assignment, vi.stubGlobal) were
patching the wrong object and failing silently.

Changes:
- setup.ts: Object.defineProperty targets window.URL so the vi.fn mock
  is visible to authUrl.ts at call time
- authUrl.test.ts: drop vi.stubGlobal approach; add vi.clearAllMocks()
  to reset accumulated call counts on the setup.ts vi.fn between tests;
  fix vi.spyOn target to window.URL in test 012

client/tests/unit/api/authUrl.test.ts

@@ -8,19 +8,9 @@ const flushPromises = () => new Promise<void>(r => setTimeout(r, 10));
 
 beforeEach(() => {
   clearImageQueue();
-  vi.restoreAllMocks(); // restore any vi.spyOn() wrappers from the previous test
-  vi.unstubAllGlobals(); // restore any vi.stubGlobal() replacements from the previous test
-
-  // jsdom's URL.createObjectURL is non-writable/non-configurable in some CI
-  // environments — direct assignment and Object.defineProperty both fail
-  // silently. vi.stubGlobal replaces globalThis.URL entirely, which always
-  // works. We extend the real URL so all URL parsing behaviour is preserved.
-  const OriginalURL = URL;
-  class TestURL extends OriginalURL {
-    static createObjectURL = vi.fn(() => 'blob:mock');
-    static revokeObjectURL = vi.fn();
-  }
-  vi.stubGlobal('URL', TestURL);
+  vi.restoreAllMocks(); // remove vi.spyOn() wrappers, restoring to the setup.ts vi.fn()
+  vi.clearAllMocks();   // reset accumulated call counts on window.URL mocks from setup.ts
+  vi.unstubAllGlobals();
 });
 
 // ── getAuthUrl ─────────────────────────────────────────────────────────────────
@@ -204,7 +194,7 @@ describe('clearImageQueue', () => {
   describe('FE-COMP-AUTHURL-012: clearImageQueue discards pending entries', () => {
     it('removes queued items so they never execute after active slots drain', async () => {
       const resolvers: Array<() => void> = [];
-      const createObjectURLSpy = vi.spyOn(URL, 'createObjectURL');
+      const createObjectURLSpy = vi.spyOn(window.URL, 'createObjectURL');
 
       vi.spyOn(globalThis, 'fetch').mockImplementation(async () => {
         await new Promise<void>(r => resolvers.push(r));