Fix script/convert for new monorepo structure

The script/convert tool is used by CI 'minimum' dependency tests to downgrade
to minimum supported versions (Ruby 3.2, Node 20, Shakapacker 8.2.0, React 18).

After the monorepo restructure (PR #2112), the script was failing because it was
looking for spec/dummy/package.json at the old root location, but these files are
now under react_on_rails/spec/dummy/ and react_on_rails_pro/spec/dummy/.

Updated all file path references:
- spec/dummy/package.json → react_on_rails/spec/dummy/package.json
- spec/dummy/config/shakapacker.yml → react_on_rails/spec/dummy/config/shakapacker.yml

Fixes CI failure:
https://github.com/shakacode/react_on_rails/actions/runs/19624872033/job/56191736323

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

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

Author: justin808

script/convert

@@ -15,11 +15,11 @@ def move(old_path, new_path)
 end
 
 # Keep shakapacker.yml since we're using Shakapacker 8+
-# move("../spec/dummy/config/shakapacker.yml", "../spec/dummy/config/webpacker.yml")
+# move("../react_on_rails/spec/dummy/config/shakapacker.yml", "../react_on_rails/spec/dummy/config/webpacker.yml")
 
 # Shakapacker - use version with async script loading support (8.2.0+)
 gsub_file_content("../Gemfile.development_dependencies", /gem "shakapacker", "[^"]*"/, 'gem "shakapacker", "8.2.0"')
-gsub_file_content("../spec/dummy/package.json", /"shakapacker": "[^"]*",/, '"shakapacker": "8.2.0",')
+gsub_file_content("../react_on_rails/spec/dummy/package.json", /"shakapacker": "[^"]*",/, '"shakapacker": "8.2.0",')
 
 # The below packages don't work on the oldest supported Node version and aren't needed there anyway
 # Note: All dev dependencies remain in root package.json even after workspace migration
@@ -36,8 +36,8 @@ gsub_file_content("../package.json", /,(\s*})/, "\\1")
 # Switch to minimum supported React version (React 18 since we removed PropTypes)
 gsub_file_content("../package.json", /"react": "[^"]*",/, '"react": "18.0.0",')
 gsub_file_content("../package.json", /"react-dom": "[^"]*",/, '"react-dom": "18.0.0",')
-gsub_file_content("../spec/dummy/package.json", /"react": "[^"]*",/, '"react": "18.0.0",')
-gsub_file_content("../spec/dummy/package.json", /"react-dom": "[^"]*",/, '"react-dom": "18.0.0",')
+gsub_file_content("../react_on_rails/spec/dummy/package.json", /"react": "[^"]*",/, '"react": "18.0.0",')
+gsub_file_content("../react_on_rails/spec/dummy/package.json", /"react-dom": "[^"]*",/, '"react-dom": "18.0.0",')
 gsub_file_content(
   "../packages/react-on-rails-pro/package.json",
   /"test:non-rsc": "(?:\\"|[^"])*",/,