Well first of note, but is not related to this issue, you can put your “sass-brunch” line in the package.json file in the devDependencies section instead of dependencies, but that will not cause an issue regardless. 
Second, your file is including foundation.scss, successfully, but the foundation.scss is including this:
However, as you can see here:
There is no normalize-scss file in their repository. For note, normalize-scss is usually included by https://www.npmjs.com/package/normalize-scss, and by looking it seems they do have that set as a dependency:
https://github.com/zurb/foundation-sites/blob/develop/package.json#L20
However your sass include definitions is only this:
sass: {
options: {
includePaths: [
'node_modules/foundation-sites/scss',
'node_modules/motion-ui/src',
]
}
}
You are not including the normalize-css modules, so you probably need to change it to this:
sass: {
options: {
includePaths: [
'node_modules/normalize-scss/sass',
'node_modules/foundation-sites/scss',
'node_modules/motion-ui/src',
]
}
}
So, does that work?
