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/timeline/CMakeLists.txt

@@ -17,6 +17,7 @@
 
 set(OLIVE_SOURCES
         ${OLIVE_SOURCES}
+        timeline/timelinecommonapp.h
         timeline/timelinecoordinate.h
         timeline/timelinecoordinate.cpp
         PARENT_SCOPE

app/timeline/timelinecommonapp.h

@@ -0,0 +1,70 @@
+/***
+
+  Oak - Non-Linear Video Editor
+  Copyright (C) 2026 Oak Team
+
+  This program is free software: you can redistribute it and/or modify
+  it under the terms of the GNU General Public License as published by
+  the Free Software Foundation, either version 3 of the License, or
+  (at your option) any later version.
+
+  This program is distributed in the hope that it will be useful,
+  but WITHOUT ANY WARRANTY; without even the implied warranty of
+  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+  GNU General Public License for more details.
+
+  You should have received a copy of the GNU General Public License
+  along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+***/
+
+#ifndef OAK_TIMELINECOMMONAPP_H
+#define OAK_TIMELINECOMMONAPP_H
+
+#include <olive/core/core.h>
+
+typedef struct OakEngineTrack OakEngineTrack;
+typedef struct OakEngineBlock OakEngineBlock;
+
+namespace olive
+{
+
+using olive::core::Rational;
+
+/**
+ * @brief App-side mirror of engine's olive::Timeline
+ * (engine/timeline/timelinecommon.h).
+ *
+ * Pure enums + a POD struct, identical to the engine version. It is named
+ * TimelineApp (not Timeline) because the engine class still reaches some
+ * app translation units transitively (e.g. via engine/node/block/block.h)
+ * and an identical name would be an ODR redefinition there.
+ *
+ * Enumerator ordinals must stay in sync with the engine enums: the C ABI
+ * transports these values as ints (OAKENGINE_MOVEMENT_MODE_* in
+ * oakengine/timeline.h, the `movement_mode` parameter of
+ * oakengine_block_trim_command(), etc.).
+ */
+class TimelineApp {
+public:
+	enum MovementMode { k_none, k_move, k_trim_in, k_trim_out };
+
+	enum ThumbnailMode { k_thumbnail_off, k_thumbnail_in_out, k_thumbnail_on };
+
+	enum WaveformMode { k_waveforms_disabled, k_waveforms_enabled };
+
+	static bool is_a_trim_mode(MovementMode mode)
+	{
+		return mode == k_trim_in || mode == k_trim_out;
+	}
+
+	struct EditToInfo {
+		OakEngineTrack *track;
+		Rational nearest_time;
+		OakEngineBlock *nearest_block;
+	};
+};
+
+}
+
+#endif // OAK_TIMELINECOMMONAPP_H

app/timeline/timelinecoordinate.cpp

@@ -25,19 +25,19 @@ namespace olive
 {
 
 TimelineCoordinate::TimelineCoordinate()
-	: track_(Track::k_none, 0)
+	: track_(TrackReference::k_none, 0)
 {
 }
 
 TimelineCoordinate::TimelineCoordinate(const Rational &frame,
-									   const Track::Reference &track)
+									   const TrackReference &track)
 	: frame_(frame)
 	, track_(track)
 {
 }
 
 TimelineCoordinate::TimelineCoordinate(const Rational &frame,
-									   const Track::Type &track_type,
+									   const TrackReference::Type &track_type,
 									   const int &track_index)
 	: frame_(frame)
 	, track_(track_type, track_index)
@@ -49,7 +49,7 @@ const Rational &TimelineCoordinate::get_frame() const
 	return frame_;
 }
 
-const Track::Reference &TimelineCoordinate::get_track() const
+const TrackReference &TimelineCoordinate::get_track() const
 {
 	return track_;
 }
@@ -59,7 +59,7 @@ void TimelineCoordinate::set_frame(const Rational &frame)
 	frame_ = frame;
 }
 
-void TimelineCoordinate::set_track(const Track::Reference &track)
+void TimelineCoordinate::set_track(const TrackReference &track)
 {
 	track_ = track;
 }

app/timeline/timelinecoordinate.h

@@ -22,28 +22,32 @@
 #ifndef OAK_TIMELINECOORDINATE_H
 #define OAK_TIMELINECOORDINATE_H
 
-#include "node/output/track/track.h"
+#include <olive/core/util/rational.h>
+
+#include "common/trackreferencehandle.h"
 
 namespace olive
 {
 
+using namespace core;
+
 class TimelineCoordinate {
 public:
 	TimelineCoordinate();
-	TimelineCoordinate(const Rational &frame, const Track::Reference &track);
-	TimelineCoordinate(const Rational &frame, const Track::Type &track_type,
+	TimelineCoordinate(const Rational &frame, const TrackReference &track);
+	TimelineCoordinate(const Rational &frame, const TrackReference::Type &track_type,
 					   const int &track_index);
 
 	const Rational &get_frame() const;
-	const Track::Reference &get_track() const;
+	const TrackReference &get_track() const;
 
 	void set_frame(const Rational &frame);
-	void set_track(const Track::Reference &track);
+	void set_track(const TrackReference &track);
 
 private:
 	Rational frame_;
 
-	Track::Reference track_;
+	TrackReference track_;
 };
 
 }