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/packaging/arch/PKGBUILD.in

@@ -6,7 +6,7 @@ pkgdesc="Oak - Non-linear video editor"
 arch=('x86_64')
 url="https://oakvideoeditor.org"
 license=('GPL3')
-depends=('qt6-base' 'qt6-tools' 'ffmpeg' 'openimageio' 'opencolorio' 'openexr' 'expat' 'portaudio' 'mesa' 'vulkan-icd-loader' 'libxkbcommon' 'fmt')
+depends=('qt6-base' 'qt6-tools' 'ffmpeg' 'openimageio' 'opencolorio' 'openexr' 'expat' 'portaudio' 'mesa' 'vulkan-icd-loader' 'libxkbcommon' 'fmt' 'opentimelineio')
 makedepends=('cmake' 'ninja' 'git' 'pkgconf' 'vulkan-headers')
 source=("${pkgname}-${pkgver}.tar.gz")
 md5sums=('SKIP')
@@ -16,6 +16,7 @@ build() {
   cmake -S . -B build -G Ninja \
     -DCMAKE_BUILD_TYPE=Release \
     -DCMAKE_INSTALL_PREFIX=/usr \
+    -DOAK_BUNDLE_OTIO=OFF \
     -DBUILD_QT6=ON
   cmake --build build
 }