Migrate apps/central SCSS to modern Sass

[latin-panda]

Description

When attempting to upgrade the SASS minor version, over 2,000 warnings are generated during the test suite execution. This massive influx of warnings causes the tests to fail entirely.

npm run test -w=@getodk/central-frontend

Output:

WARNING: Module Warning (from ../../node_modules/sass-loader/dist/cjs.js):
WARNING: Module Warning (from ../../node_modules/sass-loader/dist/cjs.js):
...
WARNING: WARN LOG: '[intlify] 'tc' and '$tc' has been deprecated in v10. Use 't' or '$t' instead. 'tc' and '$tc’ are going to remove in v11.'
All tests passed, but there were 2234 warnings: see above.
Error: Process completed with exit code 1.

SASS has a recent deprecation of @import in favor of @use. The newer minor versions of SASS heavily flag this, flooding the console.

Also, the app/central specifies "sass": "~1". This overly broad version range automatically pulls in newer minor versions that introduce these breaking deprecation warnings. It's better if this version is more specific, for example: "sass": "^1.94.2"

[matthew-white]

How hard do you think it'd be to replace @import in Central with @use? We can get someone from the Central team to do that for v2026.3 (unless you're inspired to make that change). Let us know if it'd helpful for the Central team to make that change sooner rather than later.

Also, the app/central specifies "sass": "~1". This overly broad version range automatically pulls in newer minor versions that introduce these breaking deprecation warnings. It's better if this version is more specific, for example: "sass": "^1.94.2"

I think it's nice to make it easy to upgrade to the latest version of the dependency rather than being stuck on an old version. Some of our Central dependencies are getting outdated, so it's nice not to get stuck on another old one. If we can resolve these warnings without too much trouble, how about we keep it at ~1? Otherwise we can pin it to the older version for now.

[latin-panda]

Initially, the replacement appears straightforward; I'm not sure if there will be additional issues. If no one else picks it up before I finish my assignments, I'll give it a try :)