Five documentation images, including README hero, return 404

### Describe the bug

Five `github.com/user-attachments` images referenced from the current `main` branch return HTTP 404, including the image at the top of the repository README:

| Markdown file | Broken asset |
|---|---|
| `README.md` | `26b0c2cd-70c1-4aa2-b66a-cda491ffa99c` |
| `docs/roadmap/2025-12-magic-to-do.md` | `c3857e83-eca7-4b9d-a144-4638b05af564` |
| `docs/roadmap/2025-12-magic-to-do.md` | `e2ed08a4-7eef-4adc-a540-47a45d8e5e5a` |
| `docs/roadmap/2025-12-magic-to-do.md` | `425221e9-aac0-4e5a-a115-0f8dba4cd2e7` |
| `docs/roadmap/2026-06-announcing-v2.md` | `b7f675f2-a2f1-492a-aede-199509618e77` |

### Steps to reproduce

1. Open the Markdown files above at current commit [`f1b9fb3`](https://github.com/dbt-labs/dbt-core/tree/f1b9fb34fec8074866197c7ea8d16d41fafc94cf).
2. Request any of the referenced assets, for example: https://github.com/user-attachments/assets/26b0c2cd-70c1-4aa2-b66a-cda491ffa99c
3. Observe HTTP 404 and a broken image in the rendered Markdown.

I rechecked all five URLs immediately before filing this issue.

### Expected behavior

Images referenced from versioned documentation should resolve. Ideally they should be checked into the repository (or another versioned, durable asset store) so deletion of an external attachment cannot silently break docs.

### Additional context

I found this while scanning documentation images across popular open-source repositories. The commit-pinned raw result is available in the open [docrot dataset](https://codebyaurora.com/docrot/) (generated 2026-09-11).