[FEATURE] Register a Gravatar for noreply@anthropic.com so Claude's commits have an avatar

Problem. Claude Code commits use noreply@anthropic.com (as author or in Co-Authored-By). That address has no Gravatar (https://www.gravatar.com/avatar/<md5>?d=404 returns 404), so Git clients that take avatars from Gravatar — Fork, Tower, GitKraken and others — show an empty placeholder for every Claude commit, next to human authors with pictures. Users cannot fix this themselves: only the owner of the address can attach a Gravatar to it.

Proposed solution. Register noreply@anthropic.com on gravatar.com and upload the Claude icon. It takes a few minutes and makes Claude's commits recognizable in every Gravatar-aware client, for all Claude Code users.

Context. Requested before in #18635; it was closed automatically for inactivity (not planned) and then locked, and the bot asked to open a new issue if still relevant. It is.