notification: variant icon renders invisible when the element is client-rendered (SVG children in the HTML namespace)

[eddyloewen]

Goal

The default variant icon of `el-notification` is visible whether the element was server-rendered or created in the browser.

Context

`variantIconTemplate()` nests a template result (`${paths[this.variant] ?? info}`) inside an ``. When the element renders in the browser (a toast, or a notification added after a form action), the nested `` / `` nodes end up in the HTML namespace (`namespaceURI` is `http://www.w3.org/1999/xhtml\`), so the browser draws nothing: a 20×20 empty box. Server-rendered notifications (Declarative Shadow DOM from `@webtides/element-js-ssr-renderer`) are parsed by the browser and show the icon. Seen in loewen-digital/sveltekit-ai-starter-template (issue #10 there), where inline alerts after a form submit and all toasts lose their icon; the template slots its own icon until this is fixed.

Acceptance criteria

• A notification created with `document.createElement('el-notification')` (or rendered by a framework) shows the variant icon.
• Server-rendered notifications keep showing it.

Proposal (non-binding)

Render the whole `` per variant as one template (no nested template result inside the SVG), or create the nested nodes with `createElementNS`. This may be an element-js concern (template parts inside SVG) rather than a notification one.

Out of scope

Custom icons passed through the `icon` slot, which work.