PklBugException when given a `file:` URI with a host

Pkl currently hard-fails if given a `file:` URI with a host set.

For example:

```
pkl eval file://example.com/bar/baz.pkl
```

Produces:

```
An unexpected error has occurred. Would you mind filing a bug report?
```

We should either support remote files, or throw a meaningful error here.

Start by reproducing the failure with `pkl eval file://example.com/bar/baz.pkl`, then trace the CLI's handling of `file:` URIs. Determine whether the project has an established direction for remote files; done means either remote files work or this input produces a meaningful, intentional error instead of `PklBugException`.

Written by the indexing model from the issue text.