In-place control value updates — Visualizer.set_control_value and
Visualizer.set_control_view_value (plus VizSceneHandle.set_control_value)
update a control's value after creation via a lightweight control_update
message, preserving panel collapse/drag/focus state instead of rebuilding.
Value-edit (stepper) control — add_value_edit / ValueEditView add a
numeric stepper with min/max/step/digits, up/down buttons,
arrow-key / scroll-wheel stepping, and optional direct text editing
(editable=True).
default renamed to value — the control value field is now value
everywhere: the Slider / Dropdown / ColorPicker / Checkbox
dataclasses, the SliderView / DropdownView / ColorPickerView /
CheckboxView layout controls, the add_slider / add_dropdown /
add_color_picker / add_checkbox APIs, and the serialized "value" wire
field. The old default= keyword no longer works.