fix(issue): show merged pull requests as merged in issue lists and search

issue list --kind all, milestone issue list and search pr reported a
merged pull request as closed. Their state is now merged, in tables and
in JSON, which also tells issues and pull requests apart by kind.

Signed-off-by: bircni <bircni@icloud.com>

internal/services/issues.go

@@ -39,16 +39,25 @@ const (
 	KindPull  = "pull"
 )
 
-// discussionFrom converts an issue or a pull request listed among issues.
+// discussionFrom converts an issue or a pull request listed among issues; the state of a merged
+// pull request is "merged" rather than "closed".
 func discussionFrom(issue *gitea.Issue) Issue {
 	item := issueFrom(issue)
-	item.Kind = KindIssue
+	item.Kind, item.State = KindIssue, discussionState(issue)
 	if issue.PullRequest != nil {
 		item.Kind = KindPull
 	}
 	return item
 }
 
+// discussionState is the state of an issue, or "merged" for a merged pull request.
+func discussionState(issue *gitea.Issue) string {
+	if issue.PullRequest != nil && issue.PullRequest.HasMerged {
+		return "merged"
+	}
+	return string(issue.State)
+}
+
 // IssueMilestone identifies the milestone associated with an issue or pull request.
 type IssueMilestone struct {
 	ID    int64  `json:"id"`