Restore Rainbow colors and SKIP_VALIDATION to generator template

Restored the original implementation which had:
1. Rainbow colored output for better UX during builds
2. ENV["REACT_ON_RAILS_SKIP_VALIDATION"] = "true" because this hook
   loads Rails environment and validation would fail during builds

The SKIP_VALIDATION is needed here because:
- The hook loads Rails via require_relative "../config/environment"
- This triggers the engine's validation initializer
- During precompile, packages may not be fully available yet
- Setting this env var prevents spurious validation failures

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

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

Author: justin808

lib/generators/react_on_rails/templates/base/base/bin/shakapacker-precompile-hook

@@ -8,14 +8,23 @@
 # when configured in config/shakapacker.yml:
 #   precompile_hook: 'bin/shakapacker-precompile-hook'
 #
-# See: https://github.com/shakacode/shakapacker/blob/main/docs/precompile_hook.md
+# Emoji Scheme:
+#   🔄 = Running/in-progress
+#   ✅ = Success
+#   ❌ = Error
+
+# Skip validation during precompile hook execution
+# The hook runs early in the build process, potentially before full Rails initialization,
+# and doesn't need package version validation since it's part of the build itself
+ENV["REACT_ON_RAILS_SKIP_VALIDATION"] = "true"
 
 require_relative "../config/environment"
 
 begin
+  puts Rainbow("🔄 Running React on Rails precompile hook...").cyan
   ReactOnRails::PacksGenerator.instance.generate_packs_if_stale
 rescue StandardError => e
-  warn "❌ Error in precompile hook: #{e.message}"
+  warn Rainbow("❌ Error in precompile hook: #{e.message}").red
   warn e.backtrace.first(5).join("\n")
   exit 1
 end