Fix Shakapacker configuration warnings

- Remove babel.config.js (unused with SWC transpiler)
- Add missing binstubs (bin/export-bundler-config)
- Update shakapacker and shakapacker-dev-server binstubs

This addresses warnings from Shakapacker's configuration validator:
- Warning about unused Babel config when using SWC transpiler
- Warning about missing export-bundler-config binstub

Note: swc-loader removal (warning #5) requires package.json changes
and should be handled separately.

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

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

Author: justin808

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__)