feat(alerts): raise one alert per open issue and pull request

Each open issue now has its own alert. An issue with recent activity is issue_fresh. An issue idle for issue_stale_after or longer is issue_stale. This replaces the single issues_stale line per repo.

A non-draft pull request younger than pr_warn_after now raises pr_fresh. Older pull requests keep pr_waiting.

All new alerts have warn severity, so a repo with open work is no longer green. The pr_open alert for auto actions is unchanged.

src/lib/filters.ts

@@ -24,7 +24,7 @@ export const emptyFilters = (): Filters => ({
 export function kindGroup(kind: string): KindGroup {
   if (kind.startsWith('workflow_')) return 'workflow'
   if (kind.startsWith('pr_')) return 'pr'
-  if (kind === 'issues_stale') return 'issue'
+  if (kind.startsWith('issue_')) return 'issue'
   return 'data'
 }