Component: Accordions from headings

While `details` and `summary` can provide an accordion-like experience, sometimes the markup calls for headings and associated content.

The `summary` element removes semantics of its children, so this component would progressively enhance the headings into an accordion to preserve semantics. It _augments_ rather than replaces [the existing `details` and `summary` component](https://kelpui.com/docs/components/details/).

Consider caching original heading to a data attribute for use in the `` and `` components.

Start by reading the existing details and summary component documented at kelpui.com/docs/components/details/, then inspect the kelp-toc and kelp-toc-nested entry points. The work is done when headings progressively enhance into an accordion without replacing their semantics, while the original heading is available through a data attribute for the TOC components.

Written by the indexing model from the issue text.