Fix rubocop linting issues in API chat endpoints

- Fix trailing whitespace
- Add missing final newlines
- Fix array bracket spacing
- Auto-corrected all layout issues

🤖 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
       resources :accounts, only: [ :index ]
       resources :transactions, only: [ :index, :show, :create, :update, :destroy ]
       resource :usage, only: [ :show ], controller: "usage"
-      
+
       resources :chats, only: [ :index, :show, :create, :update, :destroy ] do
         resources :messages, only: [ :create ] do
           post :retry, on: :collection