Cobra's auto-generated `completion` subcommand is undocumented and shadows the URL argument

[korya]

Problem

Cobra registers a completion subcommand by default. It is never mentioned in the README, and it takes precedence over the positional URL argument.

Reproduction

$ http-assert completion
Generate the autocompletion script for http-assert for the specified shell.
…
[exit=0]

Why it matters

The shadowing is a cosmetic edge case (a URL literally named completion is not a real scenario). The genuine gap is that shell completion exists and works but nobody knows about it.

Suggested fix

Document http-assert completion <shell> in the README installation section, or disable the subcommand via CompletionOptions.DisableDefaultCmd if it is not intended to be supported.