Add settings import to command line

# Description of the new feature/enhancement

Command line argument allowing the import of new settings files.

This would make scripting of environment setup a bit less fiddly.

Something like

```console
> wt import mySettings.json
Settings imported successfully
```

Potentially could validate settings during import to prevent overwriting existing settings with invalid ones

```console
> wt import myDodgySettings.json
Settings not valid, import failed.
Ln # 8: "HoopyFrood" is not a valid setting
Ln # 9: "KnowsWhereHisTowelIs" is an unknown value for setting "ArthurDent"
Acceptable values are "Confused", "Bewildered", or "JustWantsANiceCupOfTea".
````

If getting really fancy, the command could update valid but older settings to newer schemas

```console
> wt import myValidButOldSettings.json
Whoa, there Magrathean, those settings look a little stale!
Settings updated to new schema
Settings imported successfully
```

Start by reviewing the existing `wt` command handling and settings-file validation paths; the issue does not name specific files or tests. Compare the requested `wt import mySettings.json` behavior with current settings schema handling, including invalid and older settings, and define completion around validated imports with clear failure messages.

Written by the indexing model from the issue text.