fix: tighten error classification and pull request selection

Only Gitea's archived-repository messages mean the repository is archived,
so an archived label is no longer reported as one. Refused POSTs to the
organization, team, user and SSH key collections name the resource they would
have created, and the existing pull request is looked up with escaped branch
names.

pullSelector without an argument refuses an explicit --repo, like gh: the
checked-out branch says nothing about another repository.

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

internal/app/download.go

@@ -5,6 +5,7 @@ package app
 
 import (
 	"bufio"
+	"cmp"
 	"errors"
 	"fmt"
 	"io"
@@ -58,10 +59,10 @@ func (f downloadFlags) destination(name string) (path string, skip bool, err err
 	}
 	path = f.output
 	if path == "" || isDirectory(path) {
-		if name != filepath.Base(name) || name == "." || name == ".." || strings.ContainsAny(name, `/\`) {
+		if name == "" || name == "." || name == ".." || strings.ContainsAny(name, `/\`) {
 			return "", false, clierr.Wrap(clierr.Usage, fmt.Errorf("cannot use %q as a file name; pass --output", name))
 		}
-		path = filepath.Join(cmpOrDot(path, f.dir), name)
+		path = filepath.Join(cmp.Or(path, f.dir, "."), name)
 	}
 	if _, err := os.Lstat(path); err == nil {
 		if f.skipExisting {
@@ -76,15 +77,6 @@ func (f downloadFlags) destination(name string) (path string, skip bool, err err
 	return path, false, nil
 }
 
-func cmpOrDot(values ...string) string {
-	for _, value := range values {
-		if value != "" {
-			return value
-		}
-	}
-	return "."
-}
-
 func isDirectory(path string) bool {
 	info, err := os.Stat(path)
 	return (err == nil && info.IsDir()) || strings.HasSuffix(path, string(filepath.Separator)) || strings.HasSuffix(path, "/")