Remove Flipper and replace with ENV-driven FeatureFlags (#957)

* Presence of valid DEFAULT_UI_LAYOUT is sufficient

* Linter

config/initializers/flipper.rb

@@ -1,53 +0,0 @@
-# frozen_string_literal: true
-
-require "flipper"
-require "flipper/adapters/active_record"
-require "flipper/adapters/memory"
-
-# Configure Flipper with ActiveRecord adapter for database-backed feature flags
-# Falls back to memory adapter if tables don't exist yet (during migrations)
-Flipper.configure do |config|
-  config.adapter do
-    begin
-      Flipper::Adapters::ActiveRecord.new
-    rescue ActiveRecord::NoDatabaseError, ActiveRecord::StatementInvalid, NameError
-      # Tables don't exist yet, use memory adapter as fallback
-      Flipper::Adapters::Memory.new
-    end
-  end
-end
-
-# Initialize feature flags IMMEDIATELY (not in after_initialize)
-# This must happen before OmniAuth initializer runs
-unless Rails.env.test?
-  begin
-    # Feature flag to control SSO provider source (YAML vs DB)
-    # ENV: AUTH_PROVIDERS_SOURCE=db|yaml
-    # Default: "db" for self-hosted, "yaml" for managed
-    auth_source = ENV.fetch("AUTH_PROVIDERS_SOURCE") do
-      Rails.configuration.app_mode.self_hosted? ? "db" : "yaml"
-    end.downcase
-    default_ui_layout = ENV.fetch("DEFAULT_UI_LAYOUT", "").downcase
-
-    # Ensure feature exists before enabling/disabling
-    Flipper.add(:db_sso_providers) unless Flipper.exist?(:db_sso_providers)
-    if default_ui_layout.in?(%w[intro])
-      Flipper.add(:intro_ui, tags: [ :intro_ui ]) unless Flipper.exist?(:intro_ui)
-    end
-
-    if auth_source == "db"
-      Flipper.enable(:db_sso_providers)
-    else
-      Flipper.disable(:db_sso_providers)
-    end
-
-    if default_ui_layout.in?(%w[intro])
-      default_ui_layout == "intro" ? Flipper.enable(:intro_ui) : Flipper.disable(:intro_ui)
-    end
-  rescue ActiveRecord::NoDatabaseError, ActiveRecord::StatementInvalid
-    # Database not ready yet (e.g., during initial setup or migrations)
-    # This is expected during db:create or initial setup
-  rescue StandardError => e
-    Rails.logger.warn("[Flipper] Error initializing feature flags: #{e.message}")
-  end
-end