fix(tests): resolve URL.createObjectURL and fetch mocking failures on CI

Three interrelated issues caused 4 tests to pass locally but fail on CI:

1. setup.ts only applied the URL.createObjectURL stub when it was
   undefined, but jsdom already defines it (returning ''). Changed to
   always override with configurable:true so the predictable 'blob:mock'
   value is set in every environment.

2. FE-API-013 used Object.defineProperty (non-configurable in jsdom) and
   MSW to handle a native fetch call. Replaced with vi.spyOn for both
   URL.createObjectURL/revokeObjectURL and a direct fetch mock, which is
   more reliable across environments.

3. FE-COMP-AUTHURL-012's vi.spyOn(URL, 'createObjectURL') returned the
   same vi.fn() instance set in setup.ts, accumulating calls from all
   prior tests in the file (1+8+7+6=22 instead of 6). Added mockClear()
   immediately after the spy setup to reset the count.

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

@@ -193,6 +193,7 @@ describe('clearImageQueue', () => {
     it('removes queued items so they never execute after active slots drain', async () => {
       const resolvers: Array<() => void> = [];
       const createObjectURLSpy = vi.spyOn(URL, 'createObjectURL');
+      createObjectURLSpy.mockClear(); // vi.spyOn returns the same vi.fn() set in setup.ts; reset accumulated calls from prior tests
 
       vi.spyOn(globalThis, 'fetch').mockImplementation(async () => {
         await new Promise<void>(r => resolvers.push(r));