engine: add init/project/timeline families to the C ABI facade
- oakengine_init/shutdown with HEADLESS/RENDER flags: headless boots
Config, NodeFactory, ColorManager, task/conform/proxy/frame/disk
managers and the serializer (plus an offscreen QGuiApplication that
Qt requires for QAction); RENDER adds RenderManager. Idempotent and
upgradable, no UI anywhere
- oakengine_project_* (17): create/load/save, modified state, name,
footage enumeration with online check, undo/redo, sequence access
- oakengine_sequence_* (13): name, length (seconds and rational),
frame rate, per-type track counts, playhead (timestamp and seconds),
work area, markers; sequences are borrowed handles owned by their
project
- pure-C oakengine_init_test covers init idempotency, save/load
round-trip through a real fixture project, footage online checks,
timeline parameters, and NULL/bounds safety - no GL required
Mike-Solar
5db7aac058