Add mode option to wxt prepare command

Feature Request

The build, zip, and dev commands all support passing the mode flag, but the prepare command does not.

In my chrome extension, I have different behavior for building the manifest in production vs development environments. In prod environments, I am fetching secrets that are not allowed to be fetched in other environments.

When my team runs prepare locally or in CI to type-check the project, the script fails because the buildManifest function is run in production mode and attempts to fetch secrets that are not allowed.

Allowing devs to pass --mode to prepare would align it with the behavior of the other scripts that are needed for local development and provide a clean solution to this problem.

Is your feature request related to a bug?

No

What are the alternatives?

As a workaround, I am setting NODE_ENV to development and then checking if the mode is production and the NODE_ENV is development to know that we are running in the prepare script.

The alternative solution for the wxt project is to skip building the manifest when running prepare.

Additional context

The documentation could be a little bit clearer on this:

By default, --mode is development for the dev command and production for all other commands (build, zip, etc).

The "etc." here implies that there are commands other than dev, build, and zip which support the --mode flag, but actually only those three support it and the others are always production.

https://wxt.dev/guide/essentials/config/build-mode.html#build-modes

Also, thank you for all the work on this project. It has been a joy to work with wxt.

Start at the prepare command implementation and compare how the build, zip, and dev commands parse and apply the mode flag. The work is done when prepare accepts --mode consistently and the build-mode documentation accurately lists which commands support it.