cli: help and usage print the command as typed #267

CLI help and usage show the server's command path, not the one typed.

• gitbay auth keys --help prints USAGE ssh git@gitbay.org keys <verb> ...; gitbay auth token --help prints ssh git@gitbay.org token <verb>.
• gitbay auth keys remove with no argument prints usage: keys remove <fingerprint>.
• Every verb's usage shows <owner/name> as required, though the CLI infers it inside a clone.
• gitbay auth keys add --help and pgp add --help print unknown flag "--help" and exit 2: their RunE closures in cmd/gitbay/main.go (around lines 432 and 452) go straight to stdinPayload without the --help check pass() has.
• Two help layouts: gitbay auth --help is cobra's, gitbay notifications --help is the registry's.
• Some summaries are bare nouns (issue assign → "assignees", issue comment → "comment").

Decided: when the call comes from the CLI, help and usage print the CLI form.

• The CLI sends its invoking path with --term; the server prints gitbay auth keys remove <fingerprint> for it and the ssh git@host keys remove form for stock OpenSSH.
• [<owner/name>] shown as optional from the CLI.
• --help check in the keys add and pgp add closures.
• Render the auth group with the registry layout.
• Verb-phrase summaries: "add or remove assignees", "add a comment", "add or remove labels".