Remove external service dependencies in migration tests (#36866)

Fix #36859

Replace live third-party API calls in migration tests with a
fixture-based HTTP mock server. Fixtures are committed so tests run
offline by default; live recording is gated per service on an API-token
env var.

Co-authored-by: Claude (Opus 4.7) <noreply@anthropic.com>

services/migrations/main_test.go

@@ -25,8 +25,7 @@ func assertTimeEqual(t *testing.T, expected, actual time.Time) {
 func assertTimePtrEqual(t *testing.T, expected, actual *time.Time) {
 	if expected == nil {
 		assert.Nil(t, actual)
-	} else {
-		assert.NotNil(t, actual)
+	} else if assert.NotNil(t, actual) {
 		assertTimeEqual(t, *expected, *actual)
 	}
 }