Use exact option in package_json gem for installing dependencies

The package_json gem (v0.2.0) now supports an 'exact' parameter in the add
method to install packages with exact versions (no ^ or ~ prefix). This change
updates the add_npm_dependencies helper method to use exact: true when adding
both regular and dev dependencies.

This ensures that React on Rails generators install npm packages with exact
version specifications, consistent with the project's requirement for strict
version matching between the gem and npm packages.

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

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

Author: justin808

lib/generators/react_on_rails/generator_helper.rb

@@ -26,9 +26,9 @@ def add_npm_dependencies(packages, dev: false)
 
     begin
       if dev
-        pj.manager.add(packages, type: :dev)
+        pj.manager.add(packages, type: :dev, exact: true)
       else
-        pj.manager.add(packages)
+        pj.manager.add(packages, exact: true)
       end
       true
     rescue StandardError => e