fix(pr): refuse pr comment and pr attachment on issues

Gitea serves pull request comments and attachments through issue
endpoints, so tea pr comment create 1 posted on issue #1. pr comment and
pr attachment commands now check that the number is a pull request, and
comment IDs that the comment is on one, and point at the issue command
otherwise: "#1 in alice/project is an issue, not a pull request; use tea
issue comment create 1". Issues gain a kind field (issue or pull) in JSON.

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

internal/app/issue_attachments_test.go

@@ -21,6 +21,8 @@ func TestAttachmentCommandsShareIssueAssetsAndPagination(t *testing.T) {
 			_, _ = w.Write([]byte(`[{"id":1,"name":"one"},{"id":2,"name":"two"}]`))
 		case "/api/v1/repos/alice/project/issues/1/assets/1":
 			_, _ = w.Write([]byte(`{"id":1,"name":"one"}`))
+		case "/api/v1/repos/alice/project/issues/1":
+			_, _ = w.Write([]byte(`{"number":1,"pull_request":{}}`))
 		default:
 			t.Fatalf("unexpected path %s", r.URL.Path)
 		}
@@ -43,6 +45,10 @@ func TestAttachmentRenameAndConfirmedDeletion(t *testing.T) {
 	for _, group := range []string{"issue", "pr"} {
 		mutations := 0
 		server := newAuthenticatedServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+			if r.Method == http.MethodGet && r.URL.Path == "/api/v1/repos/alice/project/issues/1" {
+				_, _ = w.Write([]byte(`{"number":1,"pull_request":{}}`))
+				return
+			}
 			require.Equal(t, "/api/v1/repos/alice/project/issues/1/assets/1", r.URL.Path)
 			mutations++
 			if r.Method == http.MethodPatch {