refactor: ⚡ Username and slug unique indexes, before actions for set link and user

confirm_password_validation around action, unnecessary helpers removed, rubocop-rails suggestions applied

Add username index and unique slug index migrations

app/controllers/users_controller.rb

@@ -1,22 +1,29 @@
 # frozen_string_literal: true
 
 class UsersController < ApplicationController
-  def create
-    if user_params[:password] != params[:user][:confirm_password]
-      return render json: { password: ['Password not match with Confirm Password'] }, status: :bad_request
-    end
+  around_action :confirm_password_validation, only: %i[create]
 
+  def create
     @user = User.create(user_params)
     if @user.errors.any?
       render json: @user.errors, status: :unprocessable_entity
     else
       session[:user_id] = @user.id
+      session[:username] = @user.username
       render json: nil, status: :ok
     end
   end
 
   private
 
+  def confirm_password_validation
+    if user_params[:password] == params[:user][:confirm_password]
+      yield
+    else
+      render json: { password: ['Password not match with Confirm Password'] }, status: :bad_request
+    end
+  end
+
   def user_params
     params.require(:user).permit(:username, :password)
   end