Realistic demo data for performance testing (#2361)

* Realistic demo data for performance testing

* Add note about performance testing

* Fix bugbot issues

* More realistic account values

app/models/demo/data_cleaner.rb

@@ -0,0 +1,31 @@
+# SAFETY: Only operates in development/test environments to prevent data loss
+class Demo::DataCleaner
+  SAFE_ENVIRONMENTS = %w[development test]
+
+  def initialize
+    ensure_safe_environment!
+  end
+
+  # Main entry point for destroying all demo data
+  def destroy_everything!
+    puts "Clearing existing data..."
+
+    # Rails associations handle cascading deletes
+    Family.destroy_all
+    Setting.destroy_all
+    InviteCode.destroy_all
+    ExchangeRate.destroy_all
+    Security.destroy_all
+    Security::Price.destroy_all
+
+    puts "Data cleared"
+  end
+
+  private
+
+    def ensure_safe_environment!
+      unless SAFE_ENVIRONMENTS.include?(Rails.env)
+        raise SecurityError, "Demo::DataCleaner can only be used in #{SAFE_ENVIRONMENTS.join(', ')} environments. Current: #{Rails.env}"
+      end
+    end
+end