Fix SCSS undefined variable error by importing app-variables

Add @import statement to HelloWorld.module.scss files to import
app-variables.scss which defines $bright-color variable. This fixes
the "Undefined variable" SCSS compilation error during webpack builds.

Fixed in both:
- spec/dummy/client/app/components/HelloWorld.module.scss
- react_on_rails_pro/spec/dummy/client/app/components/HelloWorld.module.scss

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <[email protected]>

Author: justin808

react_on_rails_pro/spec/dummy/client/app/components/HelloWorld.module.scss

@@ -1,3 +1,5 @@
+@import "../assets/styles/app-variables.scss";
+
 .brightColor {
   color: $bright-color;
 }

spec/dummy/client/app/components/HelloWorld.module.scss

@@ -1,3 +1,5 @@
+@import "../assets/styles/app-variables.scss";
+
 .brightColor {
   color: $bright-color;
 }