Issue link should be clickable in `@githubpr` chat output

I've been chatting with `@githubpr` about my PR and what it knows.

It'd be great for the issue number `7280` at the end to be clickable:

<img width="837" height="1474" alt="Image" src="https://github.com/user-attachments/assets/511fe934-7bef-4638-af94-8423eb2a6e47" />