[feat] Integrate header registry with all HTTP clients

- Replace direct fetch() with fetchWithHeaders across entire codebase
- Replace axios.create() with createAxiosWithHeaders in all services
- Update tests to properly mock network client adapters
- Fix hoisting issues in test mocks for axios instances
- Ensure all network calls now support header injection

This completes Step 2: integrating the header registry infrastructure with all existing HTTP clients in the codebase.

tests-ui/tests/services/customerEventsService.test.ts

@@ -27,6 +27,11 @@ vi.mock('axios', () => ({
   }
 }))
 
+// Mock networkClientAdapter to return the same axios instance
+vi.mock('@/services/networkClientAdapter', () => ({
+  createAxiosWithHeaders: vi.fn(() => mockAxiosInstance)
+}))
+
 vi.mock('@/stores/firebaseAuthStore', () => ({
   useFirebaseAuthStore: vi.fn(() => mockFirebaseAuthStore)
 }))