Fix aggregate SCSS lint task (#3453)

### Summary

Fixes `rake lint` so the SCSS step uses the existing `pnpm run
lint:scss` package script instead of calling a missing `pnpm run
stylelint` script directly.
This keeps the aggregate local lint workflow aligned with the
repository's package scripts.

### Pull Request checklist

- ~[x] Add/update test to cover these changes~
- ~[x] Update documentation~
- ~[x] Update CHANGELOG file~

### Other Information

Validated with `rake lint`, `(cd react_on_rails && bundle exec
rubocop)`, and the commit/push hooks.

<!-- CURSOR_SUMMARY -->
---

> [!NOTE]
> **Low Risk**
> Single-line change to which pnpm script Rake invokes for SCSS; no
runtime or security impact.
> 
> **Overview**
> **`rake lint`** and **`rake autofix`** were failing on the SCSS step
because Rake invoked a non-existent **`pnpm run stylelint`** script with
inline globs.
> 
> **`stylelint_command`** in `lint.rake` now runs **`pnpm run
lint:scss`**, matching the root **`package.json`** script and CI.
**`lint:autofix`** still passes **`--fix`** through
**`stylelint_fix_command`** unchanged.
> 
> <sup>Reviewed by [Cursor Bugbot](https://cursor.com/bugbot) for commit
f9490c4. Bugbot is set up for automated
code reviews on this repo. Configure
[here](https://www.cursor.com/dashboard/bugbot).</sup>
<!-- /CURSOR_SUMMARY -->

<!-- This is an auto-generated comment: release notes by coderabbit.ai
-->

## Summary by CodeRabbit

* **Chores**
* Updated SCSS linting to use the project's configured linting script,
ensuring consistent styling validation across the codebase.

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Author: justin808

react_on_rails/rakelib/lint.rake

@@ -37,7 +37,7 @@ namespace :lint do # rubocop:disable Metrics/BlockLength
   private
 
   def stylelint_command
-    "pnpm run stylelint \"spec/dummy/app/assets/stylesheets/**/*.scss\" \"spec/dummy/client/**/*.scss\""
+    "pnpm run lint:scss"
   end
 
   def stylelint_fix_command