R8: finish app/ pure C ABI migration (P3-P9) and make OTIO required

- app/ no longer includes engine C++ headers nor holds engine C++ types:
  engine access goes through the oakengine C ABI plus C++ wrappers
  (oakutil/oaknode.h, oakutil/oakvideo.h) and app-local mirror types
  (tooltypes, trackreferencehandle, timelinecommonapp, keyframetypes,
  subtitleapp, serializedlayoutinfoapp, nodevaluehandle, sliderdisplaytypeapp)
- engine: new C ABI functions for block/track/clip/transition navigation
  and predicates, links, caches, waveform/playback, disk folder,
  sequence_track_list, node_free, footage_is_valid, block_get_track,
  get_brush; loadotio/saveotio ported to the current engine API
- OTIO is now a required dependency: CI and CD build it on every
  platform, FindOpenTimelineIO fixed for OTIO 0.16/0.19 (the old deps
  include requirement silently disabled OTIO everywhere), runtime
  libraries are bundled into packages and copied next to macOS binaries
  (oak_copy_otio_runtime)
- fix ProjectViewModel drag&drop mime read/write size mismatch (segfault)
- unify color label naming (k_olive -> "Oak") in the app-side mirror
- docs: OTIO required, FFmpeg minimum corrected to 6.0 (en/zh)
- gtest suite: 1925 passed, 0 failed

app/dialog/progress/pluginprogressdialogreporter.cpp

@@ -33,8 +33,10 @@ PluginProgressDialogReporter::PluginProgressDialogReporter(
 	dialog_->setAttribute(Qt::WA_DeleteOnClose);
 	QObject::connect(dialog_, &ProgressDialog::cancelled, dialog_, [this]() {
 		cancelled_ = true;
-		set_cancelled();
 	});
+	// The engine's C adapter treats show() as a no-op, so the dialog is
+	// shown here at create time.
+	dialog_->show();
 }
 
 PluginProgressDialogReporter::~PluginProgressDialogReporter()
@@ -49,18 +51,4 @@ void PluginProgressDialogReporter::set_progress(double value)
 	}
 }
 
-void PluginProgressDialogReporter::show()
-{
-	if (dialog_) {
-		dialog_->show();
-	}
-}
-
-void PluginProgressDialogReporter::close()
-{
-	if (dialog_) {
-		dialog_->close();
-	}
-}
-
 }

app/dialog/progress/pluginprogressdialogreporter.h

@@ -24,32 +24,27 @@
 
 #include <QPointer>
 
-#include "pluginSupport/pluginprogressreporter.h"
-
 namespace olive
 {
 
 class ProgressDialog;
 
 /**
- * @brief PluginProgressReporter implementation wrapping a ProgressDialog
+ * @brief ProgressDialog wrapper created through the plugin progress
+ * reporter factory
  *
- * UI-side reporter created through the plugin progress reporter factory.
- * Forwards progress calls to the dialog and the dialog's cancelled() signal
- * back to the engine. The dialog is deleted on close; the reporter itself
- * is destroyed by the engine with deleteLater().
+ * Plain UI-side class; the engine only ever talks to it through the C
+ * callbacks registered with oakengine_plugin_set_progress_reporter_factory()
+ * (create/destroy/is_cancelled/set_progress, see engine/src/capi/plugin.cpp).
+ * The dialog is shown on construction and deleted with the reporter.
  */
-class PluginProgressDialogReporter : public plugin::PluginProgressReporter {
+class PluginProgressDialogReporter {
 public:
 	PluginProgressDialogReporter(const QString &message, const QString &title);
 
-	virtual ~PluginProgressDialogReporter() override;
+	~PluginProgressDialogReporter();
 
-	virtual void set_progress(double value) override;
-
-	virtual void show() override;
-
-	virtual void close() override;
+	void set_progress(double value);
 
 	bool was_cancelled() const { return cancelled_; }