Returns the absolute selector prefix for a container — #<id> for
single-panel binds, #<id> [data-maidr-panel="<i>"] when a panel scope is
given. Binders that build custom selector strings (line, box) concatenate
this prefix with their own per-element attribute selectors.
Parameters
container: Element
The extraction root (the SVG, or a panel element).
Returns the absolute selector prefix for a container —
#<id>for single-panel binds,#<id> [data-maidr-panel="<i>"]when a panel scope is given. Binders that build custom selector strings (line, box) concatenate this prefix with their own per-element attribute selectors.