refactor: remove features beyond the UX plan

Drop additions that the UX plan does not ask for:

- the interactive label edit form; label edit now requires a flag
- label clone and the skip mode of label creation it needed
- repo rename rewriting the Git remote or tea.repository; it now
  warns that the remote still points to the old name
- the extra "source" remote on clones of pull mirrors
- run artifact download, which duplicates run download --zip
- 256-color and 24-bit label swatches; colors stay ANSI 16
- config list --show-source (config get keeps it)
- the membership and access GETs before team member/repo add and
  remove; Gitea's PUT and DELETE are idempotent

label edit/delete keep --by-name: it is the only way to address a
label whose name is a number that is also another label's ID.

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

internal/app/man_test.go

@@ -41,7 +41,7 @@ func TestManIncludesFullCommandTree(t *testing.T) {
 	deps, out, _ := testDeps(t)
 	require.NoError(t, Execute(context.Background(), deps, []string{"man"}))
 	manual := out.String()
-	for _, command := range []string{"tea-pr-checkout", "tea-issue-comment-create", "tea-auth-login", "tea-run-artifact-download"} {
+	for _, command := range []string{"tea-pr-checkout", "tea-issue-comment-create", "tea-auth-login", "tea-run-artifact-list"} {
 		require.Contains(t, manual, command)
 	}
 	require.Contains(t, manual, `.TH "TEA-PR-CHECKOUT" "1" "Jan 2026"`)