New app/playback/playbackcontroller.{h,cpp}: a lazily created
process-wide singleton whose set_playhead() forwards to
oakengine_viewer_set_playhead and re-broadcasts playhead_changed as a
plain Qt signal. Every app-side oakengine_viewer_set_playhead call site
(17 across viewer, timelinewidget, timelineview, import tool,
timebasedwidget, keyframecontrol, export dialog, mainwindow) now goes
through it.
Migrate the first four playhead subscribers off the raw C event
subscription / EngineEventBridge to the controller signal:
- TimeBasedView (issue 1)
- NodeParamViewWidgetBridge (issue 2)
- NodeParamViewKeyframeControl (issue 3)
- NodeParamViewConnectedLabel (issue 4)
Each stores a QMetaObject::Connection filtered on its viewer node and
disconnects on teardown; the viewer_sub_ members are gone. Plan docs
mark issues 0c and 1-4 as done.
Closes#30, closes#31, closes#32, closes#51, closes#52.
Mike-Solar
b77344b506