Every app module now reaches liboakengine exclusively through
oakengine_* C calls, EngineEventBridge subscriptions and app-side
handle headers (cliphandle/keyframehandle/nodevaluehandle/oakvaluehelper).
Direct C++ command construction, engine signal connect()s, and engine
type usage in MOC-visible signatures are gone: 557 -> 0 undefined
olive:: symbols in oak-editor.
- File inputs marked with the 'lut_library' property (currently the
OCIO LUT node) now show a combo box populated from the global LUT
library above the path field: pick a library LUT directly, or use
'Other (Custom File)...' with the regular path field; selections go
through the standard undoable input-change path
- Refresh zh_CN translations with lupdate and translate all strings
introduced by the proxy dialog, LUT library, LUT picker, waveform
sync and footage start time work
- Document the new per-footage custom <proxy> attributes and the
'manual' source-start-time origin in the project file reference
- Add LutFileField UI tests