fix: resolve type errors from vitest 4 Mock type changes

vi.fn() now returns Mock<Procedure | Constructable> in vitest 4, which
isn't directly callable or assignable to typed function signatures. Fix
by narrowing the mock type where it's called directly, and casting at
the assignment site for global.fetch.

apps/studio/components/interfaces/Support/__tests__/SupportFormPage.test.tsx

@@ -108,7 +108,7 @@ vi.mock(import('@/lib/breadcrumbs'), async (importOriginal) => {
 
 let createSupportStorageClientMock: ReturnType<typeof vi.fn>
 let getBreadcrumbSnapshotMock: ReturnType<typeof vi.fn>
-let generateAttachmentUrlSpy: ReturnType<typeof vi.fn>
+let generateAttachmentUrlSpy: ReturnType<typeof vi.fn<(...args: any[]) => any>>
 
 // Mock sonner toast
 vi.mock('sonner', () => ({

apps/studio/lib/ai/tools/incident-tools.test.ts

@@ -14,7 +14,7 @@ describe('ai/tools/incident-tools', () => {
   beforeEach(() => {
     vi.clearAllMocks()
     mockFetch = vi.fn()
-    global.fetch = mockFetch
+    global.fetch = mockFetch as typeof fetch
 
     // Mock AbortSignal.timeout
     mockAbortSignal = new AbortController().signal