Remove node-sass in favour of sass (Dart sass)

[rtibbles]

Description

• Replaces node-sass with sass
• Updates all @imports to @use or @forward - does not do any namespace imports for simplicity
• Fixes all calculation based deprecation warnings
• Updates deprecated function usage
• Silences the remaining js-legacy-api warnings which we can't deal with until we upgrade Vue, Nuxt, Webpack and Sass Loader (until then we're stuck where we are!)
• Adds missing @babel/preset-env dependency (I assume it had been installed by accident previously)

Issue addressed

Needed for learningequality/kolibri-ecosystem#47

Before/after screenshots

Possibly impacting every part of KDS, so will need cross checking.

Changelog

• Description: Drop node-sass in favour of sass
• Products impact: new API
• Addresses: Migrate from node-sass to sass kolibri-ecosystem#47
• Components: Affects all components through global styling tweaks.
• Breaking: yes
• Impacts a11y: no
• Guidance: Upgrading this will require using the npm sass library instead of node-sass

Steps to test

This will require fairly in depth QA, but should be sufficient within documentation for now.

(optional) Implementation notes

At a high level, how did you implement this?

Upgraded. Fixed all deprecation warnings while ensuring the build didn't break. Noting that this was mostly implemented autonomously by Claude-Code while I monitored and verified the results.

[github-actions]

Percy Visual Test Results

Percy Dashboard: View Detailed Report

Environment:

• Node.js Version: 18.x
• OS: Ubuntu-latest

Instructions for Reviewers:

• Click on the Percy Dashboard link to view detailed visual diffs.
• Review the visual changes highlighted in the report.
• Approve or request changes based on the visual differences.