[FEATURE]: Rendered components should be traceable back to the A2UI Component

In developing the [A2UI Composer](https://github.com/a2ui-project/composer), a few feature requests have come up where the user would want to select a rendered component and act on it.

The problem is, there's no way for us trace from a rendered component to the A2UI component it corresponds to.

I'm not sure how this would work in all cases, but at least for web-based renderers, if the outermost DOM element that represents the A2UI component had a `data-a2ui` property whose value is **exactly** the A2UI Component's ID, then that makes it easy. Not only is there a direct mapping, but its easy to query for DOM elements.

(For rendereed components which are from a "loop", then a few options are available; perhaps they all have the same `data-a2ui` value, with an additional `data-a2ui-instance` property to distinguish them? Or, depending on how they're rendered, perhaps there's a surrounding `div` or `span` that gets the `data-a2ui` property? Or, in the case of a list, maybe the `ol` or `ul` element gets the `data-a2ui`? Options :-))