<content-divider>

A horizontal divider: a thin rule that visually separates two pieces of
content that are not otherwise contained in a box or frame and would bleed
into each other. With a label it renders the common "─── OR ───"
pattern — text centered between two line segments; without one it is a
single full-width rule. Exposed to assistive technology as a horizontal
separator, so it renders correctly with zero external CSS.

The vertical spacing above and below is tunable per instance via
--component-divider-spacing (default 1rem), and both the plain and
labeled forms reserve the same height, so toggling the label never shifts
surrounding layout.