Update Element Settings

What it does

This ability updates an existing element's settings in place, identified by post_id and element_id (find both with premium-addons/get-page-structure), merging only the keys you pass — everything else on the element is left untouched. For v3 elements it's a flat merge into the native settings map using the same control keys premium-addons/get-widget-schema returns. For atomic (v4) elements it splits the input by whether each key is one of the type's content props (from get_props_schema(), e.g. tag, _cssid) or a CSS prop: content keys go into settings, and CSS-prop keys (kebab-case, e.g. flex-direction, background) are merged into the desktop variant of the element's existing local style class, creating one if the element doesn't have one yet. Values may be passed as plain scalars — auto-wrapped into the right atomic $$type envelope, with keys ending in "color" specifically wrapped as color values — or as pre-built { "$$type": …, "value": … } envelopes when you need a type the auto-wrap doesn't infer correctly. It refuses to modify an element whose type isn't currently registered, since Document::save() would drop it anyway. This is the single ability an AI assistant needs to restyle or reconfigure any element already on the page, atomic or classic, without recreating it.