Set inputSourceMap to undefined and disable sourceMaps

Explicitly set inputSourceMap to undefined (one of the allowed values)
and disable sourceMaps entirely to prevent babel-loader errors.

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

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

Author: justin808

config/webpack/commonWebpackConfig.js

@@ -76,7 +76,8 @@ const stimulusRule = {
   use: {
     loader: 'babel-loader',
     options: {
-      inputSourceMap: false,
+      sourceMaps: false,
+      inputSourceMap: undefined,
       presets: [
         ['@babel/preset-env', {
           useBuiltIns: 'entry',