Zsh completion broken and documentation URLs broken/removed

### Describe the bug

Before upgrading Copilot CLI today, the following snippet from my `~/.zshrc` executed as documented on https://docs.github.com/en/copilot/managing-copilot/configure-personal-settings/configuring-github-copilot-in-the-cli#zsh

```zsh
if command -v gh &>/dev/null; then
## https://docs.github.com/en/copilot/managing-copilot/configure-personal-settings/configuring-github-copilot-in-the-cli#zsh
eval "$(gh copilot alias -- zsh)"
fi
```

After upgrading to `0.0.389`, I now observe the following error message when launching a new shell:

```text
error: Invalid command format.

Did you mean: copilot -i "zsh"?

For non-interactive mode, use the -p or --prompt option.
Try 'copilot --help' for more information.
```

It would appear that the `alias` subcommand has been removed _and_ the documentation has been relocated (or entirely deleted). I can confirm that no shell completion is being automatically wired up behind the scenes—it's entirely missing/broken now.

### Affected version

0.0.389 Commit: 95ae76e

### Steps to reproduce the behavior

_No response_

### Expected behavior

_No response_

### Additional context

_No response_