Feat: Add css linting

[tuliomir]

With the new UI, the complexity of our CSS has increased and we had some hard-to-detect styling errors on our last release process ( see #356 ).

By adding a dedicated lint dependency ( Stylelint ) we increase the automated scrutinity of our code and improve its overall quality.

Acceptance Criteria

• Adds the Stylelint dependency with its default ruleset of over 100 rules
• Apply all automated changes from lint:scss:fix

Notes

The final goal of this dependency is to be added to the CI itself. However, it will require many PRs with smaller, peer reviewable changes to reach that point.

Until then, it's the developer responsibility to run the linter before merging the new feature PRs.

Security Checklist

• Make sure you do not include new dependencies in the project unless strictly necessary and do not include dev-dependencies as production ones. More dependencies increase the possibility of one of them being hijacked and affecting us.