TUI::DropdownPicker
Sizing/construction factory for a centered, content-sized Window hosting a searchable option list — the dropdown-picker counterpart to Popup.centered, except height tracks option count instead of a fixed single message line, and the "message" is an interactive list rather than static text. Push the returned Window via NavStack#push directly (same escape hatch Popup itself documents and uses), not Runtime#push, so it keeps this computed size instead of being forced full-screen.
Constants
DEFAULT_MAX_HEIGHT = 12
Default upper bound on the popup's height in rows, before the
screen-size clamp in #build_window — keeps a picker with many
options from growing to fill the whole screen. Override via
.centered/.centered_multi's max_height for a taller popup.