[Bug] Newsletter sign-up can be inserted between faux headings and images, disrupting visual flow in feature/newsletter articles

### What happened?

The newsletter sign-up component is sometimes inserted in an awkward place between a section heading and the associated image in articles that use a pattern like `

Heading

` for subheadings. This results in the sign-up breaking up what was intended to be a visually-linked heading + image pair, e.g. in [Party dresses to muddy boots: Kate Moss's best fashion moments](https://www.theguardian.com/fashion/2026/may/28/the-moments-that-made-kate-moss-a-home-grown-fashion-legend).

This pattern is used for "faux" subheadings in Composer, and those headings are indistinguishable from paragraph text for the placement algorithm. The promoted newsletter can then be inserted between a heading and its related image, disrupting the narrative flow and user experience.

#### Example URL
https://www.theguardian.com/fashion/2026/may/28/the-moments-that-made-kate-moss-a-home-grown-fashion-legend

#### Screenshots / Illustrations

### Where is this happening?

https://www.theguardian.com/fashion/2026/may/28/the-moments-that-made-kate-moss-a-home-grown-fashion-legend

### What is the impact?

- Signup can interrupt reading flow in newsletters or feature articles using bold-paragraph subheadings.
- Looks visually broken and weakens the editorial structure (heading and image are meant to form a unit).
- Editors may be unaware if they expect their headings to act as section dividers.