Add dynamic package manager detection for error messages

Detect package manager (yarn/pnpm/bun/npm) and show correct commands
in error messages instead of hardcoding yarn commands.

Detection strategy:
1. Check packageManager field in package.json (Node.js Corepack standard)
2. Fall back to lock file detection (yarn.lock, pnpm-lock.yaml, etc.)
3. Default to yarn for backward compatibility

Changes:
- Add Utils.detect_package_manager method
- Add Utils.package_manager_install_exact_command method
- Add Utils.package_manager_remove_command method
- Update all 6 error messages in VersionChecker to use dynamic commands
- Add 22 comprehensive specs with 100% coverage

Supported package managers:
- yarn: yarn add package@1.0.0 --exact
- pnpm: pnpm add package@1.0.0 --save-exact
- bun: bun add package@1.0.0 --exact
- npm: npm install package@1.0.0 --save-exact

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

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

Author: AbanoubGhadban

lib/react_on_rails/utils.rb

@@ -283,6 +283,81 @@ def self.prepend_to_file_if_text_not_present(file:, text_to_prepend:, regex:)
       puts "Prepended\n#{text_to_prepend}to #{file}."
     end
 
+    # Detects which package manager is being used.
+    # First checks the packageManager field in package.json (Node.js Corepack standard),
+    # then falls back to checking for lock files.
+    #
+    # @return [Symbol] The package manager symbol (:npm, :yarn, :pnpm, :bun)
+    def self.detect_package_manager
+      manager = detect_package_manager_from_package_json || detect_package_manager_from_lock_files
+      manager || :yarn # Default to yarn if no detection succeeds
+    end
+
+    private_class_method def self.detect_package_manager_from_package_json
+      package_json_path = File.join(Rails.root, ReactOnRails.configuration.node_modules_location, "package.json")
+      return nil unless File.exist?(package_json_path)
+
+      package_json_data = JSON.parse(File.read(package_json_path))
+      return nil unless package_json_data["packageManager"]
+
+      manager_string = package_json_data["packageManager"]
+      # Extract manager name from strings like "yarn@3.6.0" or "pnpm@8.0.0"
+      manager_name = manager_string.split("@").first
+      manager_name.to_sym if %w[npm yarn pnpm bun].include?(manager_name)
+    rescue StandardError
+      nil
+    end
+
+    private_class_method def self.detect_package_manager_from_lock_files
+      root = Rails.root
+      return :yarn if File.exist?(File.join(root, "yarn.lock"))
+      return :pnpm if File.exist?(File.join(root, "pnpm-lock.yaml"))
+      return :bun if File.exist?(File.join(root, "bun.lockb"))
+      return :npm if File.exist?(File.join(root, "package-lock.json"))
+
+      nil
+    end
+
+    # Returns the appropriate install command for the detected package manager.
+    # Generates the correct command with exact version syntax.
+    #
+    # @param package_name [String] The name of the package to install
+    # @param version [String] The exact version to install
+    # @return [String] The command to run (e.g., "yarn add react-on-rails@16.0.0 --exact")
+    def self.package_manager_install_exact_command(package_name, version)
+      manager = detect_package_manager
+
+      case manager
+      when :pnpm
+        "pnpm add #{package_name}@#{version} --save-exact"
+      when :bun
+        "bun add #{package_name}@#{version} --exact"
+      when :npm
+        "npm install #{package_name}@#{version} --save-exact"
+      else # :yarn or unknown, default to yarn
+        "yarn add #{package_name}@#{version} --exact"
+      end
+    end
+
+    # Returns the appropriate remove command for the detected package manager.
+    #
+    # @param package_name [String] The name of the package to remove
+    # @return [String] The command to run (e.g., "yarn remove react-on-rails")
+    def self.package_manager_remove_command(package_name)
+      manager = detect_package_manager
+
+      case manager
+      when :pnpm
+        "pnpm remove #{package_name}"
+      when :bun
+        "bun remove #{package_name}"
+      when :npm
+        "npm uninstall #{package_name}"
+      else # :yarn or unknown, default to yarn
+        "yarn remove #{package_name}"
+      end
+    end
+
     def self.default_troubleshooting_section
       <<~DEFAULT
         📞 Get Help & Support:

lib/react_on_rails/version_checker.rb

@@ -37,6 +37,9 @@ def validate_version_and_package_compatibility!
     def validate_package_json_exists!
       return if File.exist?(node_package_version.package_json)
 
+      base_install_cmd = ReactOnRails::Utils.package_manager_install_exact_command("react-on-rails", gem_version)
+      pro_install_cmd = ReactOnRails::Utils.package_manager_install_exact_command("react-on-rails-pro", gem_version)
+
       raise ReactOnRails::Error, <<~MSG.strip
         **ERROR** ReactOnRails: package.json file not found.
 
@@ -47,10 +50,10 @@ def validate_package_json_exists!
 
         Fix:
           1. Ensure you have a package.json in your project root
-          2. Run: yarn add react-on-rails@#{gem_version} --exact
+          2. Run: #{base_install_cmd}
 
           Or if using React on Rails Pro:
-          Run: yarn add react-on-rails-pro@#{gem_version} --exact
+          Run: #{pro_install_cmd}
       MSG
     end
 
@@ -61,6 +64,8 @@ def validate_package_gem_compatibility!
 
       # Error: Both packages installed
       if has_base_package && has_pro_package
+        remove_cmd = ReactOnRails::Utils.package_manager_remove_command("react-on-rails")
+
         raise ReactOnRails::Error, <<~MSG.strip
           **ERROR** ReactOnRails: Both 'react-on-rails' and 'react-on-rails-pro' packages are installed.
 
@@ -69,7 +74,7 @@ def validate_package_gem_compatibility!
 
           Fix:
             1. Remove 'react-on-rails' from your package.json dependencies
-            2. Run: yarn remove react-on-rails
+            2. Run: #{remove_cmd}
             3. Keep only: react-on-rails-pro
 
           #{package_json_location}
@@ -78,14 +83,17 @@ def validate_package_gem_compatibility!
 
       # Error: Pro gem but using base package
       if is_pro_gem && !has_pro_package
+        remove_cmd = ReactOnRails::Utils.package_manager_remove_command("react-on-rails")
+        install_cmd = ReactOnRails::Utils.package_manager_install_exact_command("react-on-rails-pro", gem_version)
+
         raise ReactOnRails::Error, <<~MSG.strip
           **ERROR** ReactOnRails: You have the Pro gem installed but are using the base 'react-on-rails' package.
 
           When using React on Rails Pro, you must use the 'react-on-rails-pro' npm package.
 
           Fix:
-            1. Remove the base package: yarn remove react-on-rails
-            2. Install the Pro package: yarn add react-on-rails-pro@#{gem_version} --exact
+            1. Remove the base package: #{remove_cmd}
+            2. Install the Pro package: #{install_cmd}
 
           #{package_json_location}
         MSG
@@ -94,6 +102,9 @@ def validate_package_gem_compatibility!
       # Error: Pro package but not Pro gem
       return unless !is_pro_gem && has_pro_package
 
+      remove_pro_cmd = ReactOnRails::Utils.package_manager_remove_command("react-on-rails-pro")
+      install_base_cmd = ReactOnRails::Utils.package_manager_install_exact_command("react-on-rails", gem_version)
+
       raise ReactOnRails::Error, <<~MSG.strip
         **ERROR** ReactOnRails: You have the 'react-on-rails-pro' package installed but the Pro gem is not installed.
 
@@ -105,8 +116,8 @@ def validate_package_gem_compatibility!
           2. Run: bundle install
 
         Or if you meant to use the base version:
-          1. Remove the Pro package: yarn remove react-on-rails-pro
-          2. Install the base package: yarn add react-on-rails@#{gem_version} --exact
+          1. Remove the Pro package: #{remove_pro_cmd}
+          2. Install the base package: #{install_base_cmd}
 
         #{package_json_location}
       MSG
@@ -118,6 +129,8 @@ def validate_exact_version!
       return unless node_package_version.semver_wildcard?
 
       package_name = node_package_version.package_name
+      install_cmd = ReactOnRails::Utils.package_manager_install_exact_command(package_name, gem_version)
+
       raise ReactOnRails::Error, <<~MSG.strip
         **ERROR** ReactOnRails: The '#{package_name}' package version is not an exact version.
 
@@ -128,7 +141,7 @@ def validate_exact_version!
         Do not use ^, ~, >, <, *, or other semver ranges.
 
         Fix:
-          Run: yarn add #{package_name}@#{gem_version} --exact
+          Run: #{install_cmd}
 
         #{package_json_location}
       MSG
@@ -140,6 +153,8 @@ def validate_version_match!
       return if node_package_version.parts == gem_version_parts
 
       package_name = node_package_version.package_name
+      install_cmd = ReactOnRails::Utils.package_manager_install_exact_command(package_name, gem_version)
+
       raise ReactOnRails::Error, <<~MSG.strip
         **ERROR** ReactOnRails: The '#{package_name}' package version does not match the gem version.
 
@@ -149,7 +164,7 @@ def validate_version_match!
         The npm package and gem versions must match exactly for compatibility.
 
         Fix:
-          Run: yarn add #{package_name}@#{gem_version} --exact
+          Run: #{install_cmd}
 
         #{package_json_location}
       MSG