Add .bs.js extension to resolve extensions for ReScript

Rspack needs explicit configuration to resolve ReScript compiled .bs.js files
from node_modules dependencies. Without this, ReScript library imports like
@glennsl/rescript-json-combinators fail to resolve.

This is critical for React on Rails apps using ReScript components.

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

Co-Authored-By: Claude <noreply@anthropic.com>

Author: justin808

config/rspack/commonRspackConfig.js

@@ -4,7 +4,7 @@ const { generateWebpackConfig, merge } = require('shakapacker');
 const baseClientRspackConfig = generateWebpackConfig();
 const commonOptions = {
   resolve: {
-    extensions: ['.css', '.ts', '.tsx'],
+    extensions: ['.css', '.ts', '.tsx', '.bs.js'],
   },
 };