Warn when perron:build is not run in production mode

[ianyamey]

Summary

• The set_production_env rake task from Default RAILS_ENV to production for perron:build #121 set ENV["RAILS_ENV"] but couldn't change the memoized Rails.env (which is set before any rake tasks execute), so the build still ran in development mode
• Replaces the env override with a warning message when not running in production, guiding the user to run RAILS_ENV=production bin/rails perron:build

Fixes the issue reported in #121 (comment)

Example output

❯ bin/rails perron:build
⚠️  Not running in production mode. Unpublished content will be included in the build.
 └─> Run in production mode using: RAILS_ENV=production bin/rails perron:build

🧹 Cleaning previous build…
📦 Precompiling and copying assets…
...

Test plan

• Run bin/rails perron:build without RAILS_ENV — should print a warning with the correct command
• Run RAILS_ENV=production bin/rails perron:build — should produce no warning

[eelcoj]

I like this! Bonus points for the emojis! 😄 💯

Thanks! ❤️