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/multicam/multicamdisplay.cpp

@@ -21,6 +21,8 @@
 
 #include "multicamdisplay.h"
 
+#include <QPainter>
+
 #include "oakengine/display.h"
 #include "oakengine/node.h"
 
@@ -51,7 +53,7 @@ void MulticamDisplay::on_paint()
 		int rows, cols;
 		oakengine_multicam_get_rows_and_columns(
 			oakengine_multicam_get_source_count(
-				reinterpret_cast<OakEngineNode *>(node_)),
+				node_),
 			&rows, &cols);
 
 		int multi = std::max(rows, cols);
@@ -60,7 +62,7 @@ void MulticamDisplay::on_paint()
 
 		int col, row;
 		int current_source = oakengine_multicam_get_current_source(
-			reinterpret_cast<OakEngineNode *>(node_));
+			node_);
 		oakengine_multicam_index_to_row_cols(
 			current_source, rows, cols, &row, &col);
 
@@ -211,7 +213,7 @@ QString MulticamDisplay::generate_shader_code(int rows, int cols)
 	return shader.join('\n');
 }
 
-void MulticamDisplay::set_multicam_node(MultiCamNode *n)
+void MulticamDisplay::set_multicam_node(OakEngineNode *n)
 {
 	node_ = n;
 }