Add SWC configuration for React Fast Refresh

Enable React Fast Refresh in development mode with SWC,
matching the functionality previously provided by Babel.

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

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

Author: justin808

config/swc.config.js

@@ -0,0 +1,15 @@
+const { env } = require('shakapacker');
+
+const customConfig = {
+  options: {
+    jsc: {
+      transform: {
+        react: {
+          refresh: env.isDevelopment && env.runningWebpackDevServer,
+        },
+      },
+    },
+  },
+};
+
+module.exports = customConfig;