Fix CSS Modules configuration for Shakapacker 9.x compatibility

Shakapacker 9 changed the CSS Modules default configuration from default
exports to named exports (namedExport: true). This breaks existing code
that uses `import styles from './style.module.css'` syntax.

This commit adds webpack configuration to override Shakapacker 9's CSS
Modules settings and restore backward compatibility with the v8 behavior.

Changes:
- Override namedExport: false to support default imports
- Set exportLocalsConvention: 'camelCase' to match existing usage
- Add configuration in Pro dummy commonWebpackConfig
- Matches the fix already applied to regular dummy in previous commits

This fixes CI test failures where React components weren't rendering
because CSS module imports were failing at runtime.

Related to Shakapacker upgrade from 8.0.0 to 9.1.0.

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

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

Author: justin808

react_on_rails_pro/spec/dummy/config/webpack/commonWebpackConfig.js

@@ -48,6 +48,37 @@ if (isHMR) {
   );
 }
 
-const commonWebpackConfig = () => merge({}, baseClientWebpackConfig, commonOptions, aliasConfig);
+const commonWebpackConfig = () => {
+  const config = merge({}, baseClientWebpackConfig, commonOptions, aliasConfig);
+
+  // Fix CSS modules for Shakapacker 9.x compatibility
+  // Shakapacker 9 defaults to namedExport: true, but our code uses default imports
+  // Override to use the old behavior for backward compatibility
+  config.module.rules.forEach((rule) => {
+    if (
+      rule.test &&
+      (rule.test.test('example.module.scss') || rule.test.test('example.module.css'))
+    ) {
+      if (Array.isArray(rule.use)) {
+        rule.use.forEach((loader) => {
+          if (
+            loader.loader &&
+            loader.loader.includes('css-loader') &&
+            loader.options &&
+            loader.options.modules
+          ) {
+            // Disable named exports to support default imports
+            // eslint-disable-next-line no-param-reassign
+            loader.options.modules.namedExport = false;
+            // eslint-disable-next-line no-param-reassign
+            loader.options.modules.exportLocalsConvention = 'camelCase';
+          }
+        });
+      }
+    }
+  });
+
+  return config;
+};
 
 module.exports = commonWebpackConfig;