Add red navbar background for staging environment

[Copilot]

What is the goal of this PR and why is this important?

Visual distinction between staging and production environments via navbar color. Staging shows red (bg-red-600), all other environments show blue (bg-primary).

How did you approach the change?

Added two helper methods in ApplicationHelper:

def staging_environment?
  ENV["RAILS_ENV"] == "staging" || Rails.env == "staging"
end

def navbar_bg_class
  staging_environment? ? "bg-red-600" : "bg-primary"
end

Replaced hardcoded bg-primary with <%= navbar_bg_class %> in:

• app/views/shared/_navbar.html.erb
• app/views/layouts/application.html.erb

Added test coverage for helper methods and view rendering in staging vs non-staging contexts.

Anything else to add?

Checks both ENV["RAILS_ENV"] and Rails.env to handle different deployment configurations.

Original prompt

make a pr for conditionally changing the navbar color to red when in staging (maybe based on ENV var?)

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