Stylable-button icon classes are stripped during lowering, so materialized SVG icons render at intrinsic 200x200 and bury their label

The decisive part: the generated theme CSS still ships the sizing rule, rewritten by blocks-engine to target the new structure:

```css
._icon_1fj1u_79 { min-width: 1px; ... width: var(--size); height: var(--size); ... }
._icon_1fj1u_79, :where(.data-liberation-mobile-document) :where(.blocks-engine-control-...-189.wp-block-buttons) ... ._icon_1fj1u_79 { ... }
```

The CSS was carried and rewritten; the markup that it targets was not. With no element carrying `._icon_1fj1u_79`, the `` falls back to the SVG's intrinsic `width="200" height="200"` attributes and dwarfs its own button.

## Contributing factor (tracked separately)

The capture's geometry observation for this icon is all zeros (`wrapper`/`target`/`simulated` all 0×0) because the icon is entrance-animated: Automattic/data-liberation-agent#139. A correct measurement would mask the bug on this site, but the markup/CSS mismatch above stays wrong for any control whose icon classes are stripped.

## Expected

An icon inside a lowered control keeps the classes (or equivalent sizing) that the carried stylesheet targets. Icon media must never render at intrinsic SVG canvas size when the author sized it via classes.

## Related

- Automattic/static-site-importer#1386 is the sibling failure (button collapsed to 8px on busybearscleaning.com). Both are "control lowering breaks the author's sizing contract"; the mechanism here is class stripping on icon media.

## Reproduction

Import `https://www.kdclegal.com/` and measure on the homepage:

```js
[...document.querySelectorAll('a')].filter(a => /CALL\s*US/.test(a.textContent))
.map(a => a.getBoundingClientRect())
```