Fix generator test failures by skipping validation and using exact versions

This commit fixes two issues that were causing generator tests to fail:

1. Version validation running during generator execution
   - The engine initializer was validating npm package installation
   - But generators hadn't installed packages yet (chicken-and-egg problem)
   - Solution: Skip validation when Rails generators are running

2. Package installed with semver range instead of exact version
   - package_json gem was adding packages with carets (^16.1.1)
   - React on Rails requires exact version matching between gem and npm package
   - Solution: Use npm install --save-exact directly for react-on-rails package

Changes:
- lib/react_on_rails/engine.rb: Skip validation during generator runs
- lib/generators/react_on_rails/install_generator.rb: Use --save-exact flag

Note: Filed issue with package_json gem to add exact version support:
shakacode/package_json#25

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

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

Author: justin808

lib/generators/react_on_rails/install_generator.rb

@@ -430,25 +430,20 @@ def add_js_dependencies
       def add_react_on_rails_package
         major_minor_patch_only = /\A\d+\.\d+\.\d+\z/
 
-        # Try to use package_json gem first, fall back to direct npm commands
+        # Always use direct npm install with --save-exact to ensure exact version matching
+        # The package_json gem doesn't support --save-exact flag
         react_on_rails_pkg = if ReactOnRails::VERSION.match?(major_minor_patch_only)
-                               ["react-on-rails@#{ReactOnRails::VERSION}"]
+                               "react-on-rails@#{ReactOnRails::VERSION}"
                              else
                                puts "Adding the latest react-on-rails NPM module. " \
                                     "Double check this is correct in package.json"
-                               ["react-on-rails"]
+                               "react-on-rails"
                              end
 
         puts "Installing React on Rails package..."
-        if add_npm_dependencies(react_on_rails_pkg)
-          @added_dependencies_to_package_json = true
-          return
-        end
-
-        puts "Using direct npm commands as fallback"
-        success = system("npm", "install", *react_on_rails_pkg)
+        success = system("npm", "install", "--save-exact", react_on_rails_pkg)
         @ran_direct_installs = true if success
-        handle_npm_failure("react-on-rails package", react_on_rails_pkg) unless success
+        handle_npm_failure("react-on-rails package", [react_on_rails_pkg]) unless success
       end
 
       def add_react_dependencies

lib/react_on_rails/engine.rb

@@ -13,6 +13,9 @@ class Engine < ::Rails::Engine
         package_json = VersionChecker::NodePackageVersion.package_json_path
         next unless File.exist?(package_json)
 
+        # Skip validation when running generators (packages may not be installed yet)
+        next if defined?(Rails::Generators) && ARGV.any? { |arg| arg.include?("generate") || arg.include?("g") }
+
         Rails.logger.info "[React on Rails] Validating package version and compatibility..."
         VersionChecker.build.validate_version_and_package_compatibility!
         Rails.logger.info "[React on Rails] Package validation successful"