bug: --apihost flag limitations

Description

The --apihost flag is mainly used by the maintainers of this project to test various use cases. Using it as follows --apihost=api.shhhh.slack.com mostly works as expected. But when combine with the deploy command having the api domain prefix breaks the logic that sets the SLACK_API_URL environment variable

Version

Using lack v3.3.0

OS Info

ProductName:            macOS
ProductVersion:         15.5
BuildVersion:           24F74
Darwin Kernel Version 24.5.0: Tue Apr 22 19:54:49 PDT 2025; root:xnu-11417.121.6~2/RELEASE_ARM64_T6000

Steps to reproduce:

Share the commands to run, source code, and project settings:

1. Create an app
2. Use commands with the --apihost flag set to a value prefixed with api.
   a. everything should work as expected
3. Use slack deploy --apihost=api.your.test.endpoint -vv
4. No error is raised and no trace of a request to set the SLACK_API_URL environment variable can be found
5. If the flag value is set without the api prefix the SLACK_API_URL environment variable is set and things work as expected

Expected result:

If the apihost value is rejected the CLI expects then we should inform the user

Actual result:

Nothing indicates that the apihost value is rejected by the CLI

Requirements

• I've read and understood the Contributing guidelines and have done my best effort to follow them.
• I've read and agree to the Code of Conduct.
• I've searched for any related issues and avoided creating a duplicate issue.

Start by reproducing slack deploy --apihost=api.your.test.endpoint -vv and trace the deploy command's --apihost handling and SLACK_API_URL setup. Done means the CLI either handles the api. prefix correctly or clearly informs the user that the value is rejected; verify the behavior with and without that prefix.