Fix SWC config to preserve class names for Stimulus compatibility

Add keepClassNames: true to SWC configuration to ensure Stimulus
controllers work correctly. Without this setting, class names are
mangled during transpilation, breaking Stimulus functionality.

This fixes failing RSpec tests for Turbo/Stimulus form submission.

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

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

Author: justin808

config/swc.config.js

@@ -3,6 +3,9 @@ const { env } = require('shakapacker');
 const customConfig = {
   options: {
     jsc: {
+      keepClassNames: true,
+      loose: false,
+      externalHelpers: false,
       transform: {
         react: {
           refresh: env.isDevelopment && env.runningWebpackDevServer,