ESLint - Post Upgrade Improvements

### Summary
In the [Storybook V10 upgrade PR](https://github.com/mi6/ic-ui-kit/pull/4184/changes), ESlint was upgraded too. There are a number of followup actions required:

Changes required in Eslint.config.js:
- [ ] Address the rules set to 'warn' which had to be added during the upgrade since they picked up lint failures that weren't being reported before. These should be set to error, and then errors should be fixed.
- [ ] Address the rules that were commented out. These cause TypeErrors when running the lint command itself. Fixing these might require investigation.
- [ ] convert eslint.config.js to ESM. The "require()" method of imports fails an ESlint rule.

Start with eslint.config.js and the Storybook V10 upgrade PR (PR 4184); run the lint command to reproduce the current warnings and TypeErrors. Review the warned and commented-out rules, then verify the configuration uses ESM imports and that lint completes with the intended rules enabled and no errors.

Written by the indexing model from the issue text.