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/render_diskcache_test.cpp

@@ -71,7 +71,7 @@ protected:
 			// Leaked intentionally: Core is process-wide and DiskCacheFolder
 			// eviction calls Core::instance()->WarnCacheFull() (matches
 			// viewer_display_repro_test).
-			new olive::Core(olive::Core::CoreParams());
+			new olive::Core();
 		}
 
 		olive::DiskManager::create_instance();