Feature Proposal: More stats for repo/pin cards

### Is your feature request related to a problem? Please describe.

There is a lot of data that you can gather about a repository itself besides its star count and number of forks. As opposed to thinking of a repo card as something that is sort of intrinsically related to a user, I'd like to have a proper "repo stats" card with more metrics - # of open issues, # of open PRs, age of repo, average age of open Issues, etc. - these are all meaningful indicators about the health of a repo itself.

### Describe the solution you'd like

In #4617 I've added three additional metrics to the repository/pin cards - number of open issues, number of open PRs, and age of repo. I've done this in the most minimal way I could, and it only affects the API. But as I started writing up the PR, it occurred to me that in principle a repo card could be given "first-class" status - more metrics, more customization, more flexibility for styling - effectively as flexible as the stats cards are. To me, this is something I would really be keen to know about, and to have available.

### Describe alternatives you've considered

?? I've intentionally made the PR as un-opinionated as possible because I want to know how the maintainers and the users think of repo/pin cards - are they "extras" that are not the main focus of this project, or would people be interested in having cards _about repos_ per se. Even calling them "pins" suggests that their purpose is to be pinned onto a USER's personal profile/README, rather than showing first-class metrics about a repo itself.

### Additional context

_No response_

The issue names no files or tests. Review PR #4617 and the existing repository/pin card API first; completion depends on a maintainer decision about which repository metrics, customization, and styling are in scope.

Written by the indexing model from the issue text.