mail-react: Render nested Tip-Tap list items with their own style

[VPS-Ricky]

In the admin, a content editor can give a nested list item its own style, but the mail rendered the item with the style of the item around it. A nested list has no text component of its own, so its cells copied the text styles of the enclosing item, and the responsive rules of the outermost list reached the nested cells too.

A nested item without a style now gets its list's textBlocks style, not the style of the item around it, because the admin shows it that way too.

Screenshots/screencasts

The WithListVariants story of MjmlTipTapRichTextBlock:

Before	Now

Changeset

None needed: this fixes #6406, which is not released yet.

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Task: https://vivid-planet.atlassian.net/browse/PHSB2C-12548

[VPS-Ricky]

@greptileai

[greptile-apps]

Confidence Score: 5/5

[Medium risk] Changes how nested list items render their text styles.

The PR appears safe to merge; no outstanding findings remain.

Summary

The PR makes nested Tip-Tap list items use their own text style, gives unstyled nested items their list’s default style, and scopes responsive text rules to individual rows. It also updates tests, examples, documentation, and the mail-react skill.

_{Reviews (3) · Last reviewed commit: "mail-react: Document the variant modifie..."}

[VPS-Ricky]

@greptileai

[VPS-Ricky]

@greptileai