Ctrl/Cmd+Alt dragging a selected layer bar or a selected key now runs a
Quick Offset (layer.quickOffset / keys.quickOffset with fromStart, one
undo step). The mode is chosen when the drag starts and needs at least
two unlocked layers; the last selected layer moves by whole frames with
the pointer. A readout by the pointer shows the Total Offset and the
offset Per Layer, translated.
A plain drag still moves the selection together, Alt alone still scales
a key group in time (it now leaves Ctrl/Cmd+Alt to Quick Offset), and
Ctrl/Cmd+Alt+click still toggles Hold. The key drag's readout is drawn
by a shared drag_tip. Keys also register timeline.keyAt.<uid>.<ticks>,
exact where keys on subframes can share a frame.
Tests (ui_quick_offset): staggering layer bars in selection order and
keys per layer, one undo each; plain drags and Alt scaling unchanged; the
readout while dragging.
94b4d0ca34