cli/worker/tests: facade-only linkage and updated test suites

oak-cli and oak-render-worker use the C ABI exclusively (0 olive::
symbols). Google Test suites updated for the migrated APIs, new engine
facade test coverage, CLI transcode verification.

tests/gtest/task_cache_test.cpp

@@ -90,7 +90,7 @@ protected:
 	{
 		if (!olive::Core::instance()) {
 			// Leaked intentionally: Core is process-wide (matches footage_probe_test)
-			new olive::Core(olive::Core::CoreParams());
+			new olive::Core();
 		}
 
 		olive::ColorManager::set_up_default_config();