Fix install_js_dependencies to use system() calls instead of run()

During rebase conflict resolution, the method incorrectly kept run() calls
instead of adopting master's enhanced system() calls. This was causing
CI test failures due to package manager installation issues.

Changes:
- Use system("yarn", "install") instead of run "yarn install"
- Use system("pnpm", "install") instead of run "pnpm install"
- Use system("npm", "install") instead of run "npm install"

This combines master's enhanced implementation with our method organization improvements.

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

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

Author: ihabadham

lib/generators/react_on_rails/base_generator.rb

@@ -196,13 +196,13 @@ def add_dev_dependencies
       def install_js_dependencies
         # Detect which package manager to use
         success = if File.exist?(File.join(destination_root, "yarn.lock"))
-                    run "yarn install"
+                    system("yarn", "install")
                   elsif File.exist?(File.join(destination_root, "pnpm-lock.yaml"))
-                    run "pnpm install"
+                    system("pnpm", "install")
                   elsif File.exist?(File.join(destination_root, "package-lock.json")) ||
                         File.exist?(File.join(destination_root, "package.json"))
                     # Use npm for package-lock.json or as default fallback
-                    run "npm install"
+                    system("npm", "install")
                   else
                     true # No package manager detected, skip
                   end