[BUG] Shell detection crashes when terminal default profile setting is not a string #686

Describe the bug
Zoo can crash with Provider ended the request: t.toLowerCase is not a function when the VS Code terminal default profile setting is misconfigured with a non-string value.

To Reproduce
Steps to reproduce the behavior:

1. Open VS Code settings JSON.
2. Set the terminal default profile to a non-string value. For example, on Windows:

   {
     "terminal.integrated.defaultProfile.windows": 1
   }

   Other invalid values such as true, [], or {} can also reproduce the issue.
3. Run Zoo and trigger a request that causes Zoo to resolve the shell configuration.
4. See error:

   Provider ended the request: t.toLowerCase is not a function
   

Expected behavior
Zoo should not crash when VS Code terminal profile settings contain an invalid type.

Screenshots
N/A

Video
N/A

What version of zoo are you running
3.62.0

Additional context
This seems to be a runtime type validation issue rather than a TypeScript typing issue. config.get<string>() only affects the static type, but it does not guarantee that the actual value from user settings is a string.

The current code assumes defaultProfileName is a string before calling .toLowerCase(), which can fail when the VS Code settings JSON is manually edited or corrupted.