Fix Stimulus compatibility by targeting ES6 class support

Stimulus 3 requires pure ES6 classes and cannot work when transpiled
to ES5. By adding env.targets with 'supports es6-class', we ensure
SWC doesn't downcompile classes to ES5, which was breaking the Stimulus
controller functionality.

This follows the same approach needed for TypeScript + Stimulus where
targeting ES6 explicitly is required for compatibility.

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

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

Author: justin808

config/swc.config.js

@@ -5,5 +5,8 @@ module.exports = {
         runtime: "automatic"
       }
     }
+  },
+  env: {
+    targets: "defaults and supports es6-class"
   }
 };