getMainFilePath util function fails because of hardcoded target name

### Command

add

### Description

I've seen a lot of cases when people are using different name for their build targets, for various reasons. So if the `build` is not found, the `getMainFilePath` fails, which is not right in my opinion

### Describe the solution you'd like

It should ask interactively which target should be used if `build` is not found, when interactivity is enabled in the execution context

### Describe alternatives you've considered

_No response_

Start with the getMainFilePath utility and trace how the add command handles a missing build target in an interactive execution context. Check the existing target lookup and interaction flow; done means non-build target names no longer fail silently and an interactive user can choose the target when build is absent.

索引モデルが issue の本文から書いたものです。