- effect_stack: the params view is cached per effect (recreation per
render killed in-progress slider drags and clicks); new
LibraryEffectDrag payload + AddTypeRequested event let an effect
dragged from the app's effect library drop onto the stack at the
indicator position
- timeline: left-press selects clips (plain press selects an
unselected clip, keeps multi-selection on a selected one for group
drags, Ctrl/Cmd toggles membership)
- node_graph: graph_position_at() converts a window-space point (drop
position) to graph space