Support Gravatar Hovercard for Fediverse handles in WordPress comments

# Feature Request

## Description / Use Case

Hi Automattic team,

I’d like to suggest a feature enhancement for Gravatar hovercards in the context of federated replies via ActivityPub in WordPress.

**Use case:**
When a federated reply is posted to a WordPress comment thread (for example, a reply coming from a Mastodon user via ActivityPub), and the Mastodon account’s handle (e.g., `@username@mastodon.social`) is registered in Gravatar, it would be great if WordPress could display a Gravatar Hovercard when hovering over that reply’s actor handle.

**Why this matters:**

* This would unify the identity experience across WordPress, Gravatar, and Fediverse services.
* Adds richer identity verification and social context for federated comments.
* Supports communities bridging open protocols like ActivityPub with the broader Automattic ecosystem.

**Technical notes:**
Currently, Gravatar hovercards are based on email hash lookups. This feature would require either:

* Enabling Gravatar to associate and query profiles by Fediverse handle (`@user@instance.tld`), or
* Providing a mapping mechanism within WordPress ActivityPub plugin or WordPress comment system to resolve handles to corresponding Gravatar profiles.

**Expected behavior:**
When a federated reply appears in WordPress comments:

* If the actor’s Fediverse handle is associated with a Gravatar account
* Show the Gravatar hovercard (avatar, bio, verified Fediverse handle, etc.) when hovering over the handle

This would be a valuable addition for integrating decentralized social accounts with WordPress-powered sites.

Thanks for considering this!

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Describe the feature you'd like to see added. Include the potential use case(s) to help us understand its impact.

## Proposed Solution

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## Alternatives

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## Additional Information

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The issue names no files, tests, or implementation entry points. Start by determining whether Fediverse-handle lookup belongs in Gravatar or the WordPress ActivityPub/comment integration; done would require an agreed mapping or API and the specified hovercard behavior.

Written by the indexing model from the issue text.