QbzSelectableText is a Text-shaped label the user can select and copy: a
read-only TextEdit with mouse and keyboard selection, the right-click Copy
menu, and a rich-text link for fields that navigate; its `raised` arm keeps
a plain shadowed Text for hosts on the ambient field. QbzClipboard is the
off-screen TextEdit copy carrier CommandBlock, SandboxSettings and the
lyrics flyout each grew on their own, as one primitive. QbzScrollBar gains
`alwaysShown` for surfaces that must read as scrollable.
cc
