streams: Set creator for some initial streams in populate_db.

[tnmkr]

Fixes: #29425 (comment)

Screenshots and screen captures:

Self-review checklist

• Self-reviewed the changes for clarity and maintainability
  (variable names, code reuse, readability, etc.).

Communicate decisions, questions, and potential concerns.

• Explains differences from previous plans (e.g., issue description).
• Highlights technical choices and bugs encountered.
• Calls out remaining decisions and concerns.
• Automated tests verify logic where appropriate.

Individual commits are ready for review (see commit discipline).

• Each commit is a coherent idea.
• Commit message(s) explain reasoning and motivation for changes.

Completed manual review and testing of the following:

• Visual appearance of the changes.
• Responsiveness and internationalization.
• Strings and tooltips.
• End-to-end functionality of buttons, interactions and flows.
• Corner cases, error conditions, and easily imagined bugs.

[tnmkr]

@timabbott This PR is ready for review. It is a follow up.

---

It might be worth a follow-up change to populate_db to set creators for the initial streams, which might then require changing this test.

Originally posted by @timabbott in #29425 (comment)

[timabbott]

Small comment on quoting people -- you can use GitHub's quote feature to make a more visible blockquote element.

[timabbott]

Looks great, merged, thanks @tnmkr!