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/widget/timelinewidget/tool/slip.cpp

@@ -24,7 +24,6 @@
 #include <QToolTip>
 
 #include "common/configwrapper.h"
-#include "timeline/timelineundogeneral.h"
 #include "widget/timelinewidget/timelinewidget.h"
 
 #include "oakengine/timeline.h"
@@ -76,12 +75,11 @@ void SlipTool::finish_drag(TimelineViewMouseEvent *event)
 
 	// Find earliest point to ripple around
 	foreach (TimelineViewGhostItem *ghost, parent()->get_ghost_items()) {
-		Block *b = QtUtils::value_to_ptr<Block>(
+		OakEngineBlock *b = QtUtils::value_to_ptr<OakEngineBlock>(
 			ghost->get_data(TimelineViewGhostItem::k_attached_block));
 
-		ClipBlock *cb = dynamic_cast<ClipBlock *>(b);
-		if (cb) {
-			oakengine_undo_command_multi_add_child(command, oakengine_block_set_media_in_command(reinterpret_cast<void *>(cb), ghost->get_adjusted_media_in().numerator(), ghost->get_adjusted_media_in().denominator()));
+		if (oakengine_node_is_clip(reinterpret_cast<OakEngineNode *>(b))) {
+			oakengine_undo_command_multi_add_child(command, oakengine_block_set_media_in_command(reinterpret_cast<void *>(b), ghost->get_adjusted_media_in().numerator(), ghost->get_adjusted_media_in().denominator()));
 		}
 	}