`NewsletterSignupCard` — preview modal

[georgerichmond]

Summary

Implement the preview modal triggered by the "Preview latest" CTA in NewsletterSignupCard.island.tsx. Details of the modal content and data source TBC.

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Tasks

• Implement modal trigger from "Preview latest" CTA
• Reuse existing DCR modal pattern if one exists, otherwise create new
• Wire in preview content — source TBC
• Close behaviour — click outside, escape key, explicit close button
• Storybook story for modal open state

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Open questions

• What does the modal content look like? (iframe, summary, excerpt?)
• Where does the preview content come from? (existing API endpoint or new?)
• Is there an existing modal component in DCR to reuse?

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Out of scope

• No changes to the feature flag or rollout

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Design reference

• Ensure correct designs in both light and dark mode

https://www.figma.com/design/ucERNBXZ9CAObsjnVWqgEi/Newsletter-Sign-Up-Component?node-id=1492-7289&t=9vObuzDe6UjYnHbv-11

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Want to do the already-subscribed ticket next, or the frequency one?