Fix remaining rubocop offenses

- Fix string literal style in doorkeeper.rb
- Add missing final newlines
- Remove trailing whitespace
- Fix array bracket spacing in migrations

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

Co-Authored-By: Claude <noreply@anthropic.com>

config/routes.rb

@@ -189,7 +189,7 @@ Rails.application.routes.draw do
       post "auth/signup", to: "auth#signup"
       post "auth/login", to: "auth#login"
       post "auth/refresh", to: "auth#refresh"
-      
+
       # Production API endpoints
       resources :accounts, only: [ :index ]
       resources :transactions, only: [ :index, :show, :create, :update, :destroy ]