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.
- slider DisplayType enums sink to node/sliderdisplaytype.h (canonical
engine home); FloatSlider/RationalSlider alias them for compatibility
- DropWithoutSequenceBehavior enum sinks to common/dropworkflowbehavior.h
- Config errors now go through a registered ErrorHandler hook instead of
QMessageBox with a MainWindow parent; the style default no longer
depends on the UI style manager
- MainWindowLayoutInfo moves to node/project/serializer/ and its panel
dependency is reduced to a plain std::map alias (PanelLayoutInfo),
breaking the engine -> PanelWidget -> KDDockWidgets chain
- ProjectImportErrorDialog moves from task/ to dialog/projectimport/
- remove confirmed-redundant UI includes and give project.h/import.h/
project.cpp the direct includes they were borrowing transitively
- project.h includes folder/sequence headers directly (it used both
types in its own API all along)