Newsletter: improve rendering of embed blocks

[simison]

Embeds from Twitter, TikTok, etc are currently rendered as text-only:

We'd like to be able to render something more visual in emails;

Exploration using images with our mShots API, which already has good dedicated support for Twitter embeds:

Slack convo p1726144959645139-slack-C052XEUUBL4

Came up with Team 51 customer p9MPsk-5nT-p2

Exploration in D162345-code

[dhanson-wp]

A couple more examples of wanting better email rendering.

WordPress Embed

The WordPress Embed block for internal/external site links is a nice card:

In email, the WordPress embed just looks like a Quote block:

Leveled headings in Group blocks

Designing creative patterns look great in the block editor and the frontend of posts:

In emails, while it is fine that a lot of the styles are absent (background gradient, border, etc.), the sizing and spacing of headings and text all feel off.