Backend/emails: Link user card photos to profiles

[tristanlabelle]

We trained users to expect that photos link to profiles. Emails should follow suit.

Fixes #9188

Testing

Ran uv run dump-emails

Backend checklist

• Added tests for any new code or added a regression test if fixing a bug
• Run the backend locally and it works
• Added migrations if there are any database changes, rebased onto develop if necessary for linear migration history

For maintainers

• Maintainers can push commits to my branch
• Maintainers can merge this PR for me

[CouchersBot]

Mobile

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Deep links

iOS

couchers-devtool://expo-development-client/?url=https%3A%2F%2Fd269d29e--ota.preview.couchershq.org%2Fios%2Fmanifest

Android

couchers-devtool://expo-development-client/?url=https%3A%2F%2Fd269d29e--ota.preview.couchershq.org%2Fandroid%2Fmanifest

Web (Vercel)

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Backend

Schema	Schema diff	Sample emails

Other

Protos	Backend coverage	Web coverage

[aapeliv]

lgtm and sample emails work

[github-actions]

📝 Release Notes

This PR should be included in the release notes.

Suggested release note:

Improved email user cards so profile photos now link directly to the user’s profile

🤖 Bot Debug Information

Model: couchers.openai.gpt-5.4
Decision: include
Reasoning: This is a small but noticeable user-facing usability improvement in emails: clicking a user photo in email cards now takes users directly to that profile, matching expected behavior. While minor, it improves navigation in a visible part of the product.