feat(ui): Add last validation time, disable revalidation if PR not open

• feat(ui): Add last validation time, disable revalidation if PR not open

In the status UI, previously we never stated when the last validation occurred. As we have access to this data, we should tell the user when the last validation of a commit associated with a PR happened. This better supports users to know if their failure may be due to out of date validation.

Additionally, in the case of GH PRs where we have logic to manage those calls separately, we can now check if the PR is open. We use this to now toggle whether the revalidation button will be usable and whether the hCaptcha is injected.