Keep Pro dummy app with Babel, only use SWC in spec/dummy

- Revert react_on_rails_pro/spec/dummy back to Babel transpiler
- Remove SWC config from Pro dummy app
- Update documentation to clarify only spec/dummy uses SWC
- Pro app stays with Babel for RSC stability

This provides a safer migration path where standard React on Rails apps
can benefit from SWC's 20x performance improvement, while Pro apps with
React Server Components maintain stability with Babel until SWC RSC
support matures.

Author: justin808

docs/swc-migration.md

@@ -10,6 +10,8 @@ SWC (Speedy Web Compiler) is a Rust-based JavaScript/TypeScript compiler that is
 
 ## Migration Steps
 
+**Note**: This migration has been successfully implemented in the React on Rails standard dummy app (`spec/dummy`). The Pro dummy app (`react_on_rails_pro/spec/dummy`) continues using Babel for RSC stability.
+
 ### 1. Install Required Dependencies
 
 ```bash
@@ -27,7 +29,7 @@ default: &default # Using SWC for faster JavaScript transpilation (20x faster th
 
 ### 3. Create SWC Configuration File
 
-Create `config/swc.config.js` with the following content:
+Create `config/swc.config.js` in your Rails application root with the following content:
 
 ```javascript
 const { env } = require('shakapacker');
@@ -203,7 +205,9 @@ Test coverage includes:
 
 **For React on Rails projects without React Server Components**: ✅ **Migration to SWC is recommended**
 
-**For projects using React Server Components**: ⚠️ **Proceed with caution** - consider staying with Babel until SWC RSC support stabilizes, or conduct extensive testing before production deployment.
+The standard React on Rails dummy app (`spec/dummy`) successfully uses SWC, demonstrating its compatibility with core React on Rails features.
+
+**For projects using React Server Components**: ⚠️ **Stay with Babel for now** - The React on Rails Pro dummy app continues using Babel due to RSC's experimental status with SWC. Consider staying with Babel until SWC RSC support stabilizes, or conduct extensive testing before production deployment.
 
 ## References
 

react_on_rails_pro/spec/dummy/config/shakapacker.yml

@@ -6,8 +6,7 @@ default: &default
   public_root_path: public
   public_output_path: packs
   nested_entries: true
-  # Using SWC for faster JavaScript transpilation (20x faster than Babel)
-  javascript_transpiler: swc
+  javascript_transpiler: babel
 
   cache_path: tmp/cache/webpacker
   check_yarn_integrity: false