Fix React Refresh to only enable with webpack-dev-server

- Change refresh condition from NODE_ENV === 'development' to WEBPACK_SERVE
- This ensures Fast Refresh only activates when using webpack-dev-server (bin/dev)
- Avoids unnecessary Fast Refresh transformation for static builds (bin/shakapacker)
- Matches the behavior of ReactRefreshWebpackPlugin in development.js

The WEBPACK_SERVE environment variable is set by webpack-dev-server and is the
correct indicator for when HMR and Fast Refresh should be active.

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

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

Author: justin808

spec/dummy/config/swc.config.js

@@ -8,7 +8,9 @@ module.exports = {
       react: {
         runtime: 'automatic',
         development: process.env.NODE_ENV === 'development',
-        refresh: process.env.NODE_ENV === 'development', // Enable Fast Refresh in development
+        // Only enable Fast Refresh when using webpack-dev-server (bin/dev)
+        // Not needed for static builds (bin/shakapacker)
+        refresh: !!process.env.WEBPACK_SERVE,
       },
     },
   },