Fix Shakapacker configuration warnings

- Remove babel.config.js (unused with SWC transpiler)
- Remove swc-loader from package.json (built into Rspack)
- Add bin/export-bundler-config binstub
- Update bin/shakapacker and bin/shakapacker-dev-server binstubs
- Add shakapacker-config-exports/ to .gitignore

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

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

Author: justin808

demos/basic-v16-rspack/.gitignore

@@ -23,6 +23,7 @@ coverage/
 # Shakapacker compiled assets
 /public/packs/
 /public/packs-test/
+/shakapacker-config-exports/
 
 # Node
 /node_modules/

demos/basic-v16-rspack/babel.config.js

@@ -0,0 +1,11 @@
+#!/usr/bin/env node
+
+// Minimal shim - all logic is in the TypeScript module
+const { run } = require('shakapacker/configExporter')
+
+run(process.argv.slice(2))
+  .then((exitCode) => process.exit(exitCode))
+  .catch((error) => {
+    console.error(error.message)
+    process.exit(1)
+  })

demos/basic-v16-rspack/bin/export-bundler-config

@@ -1,5 +1,4 @@
 #!/usr/bin/env ruby
-# frozen_string_literal: true
 
 ENV["RAILS_ENV"] ||= "development"
 ENV["BUNDLE_GEMFILE"] ||= File.expand_path("../Gemfile", __dir__)

demos/basic-v16-rspack/bin/shakapacker

@@ -1,5 +1,4 @@
 #!/usr/bin/env ruby
-# frozen_string_literal: true
 
 ENV["RAILS_ENV"] ||= "development"
 ENV["BUNDLE_GEMFILE"] ||= File.expand_path("../Gemfile", __dir__)