feat: create User and Import models with business logic

- User model with role management (admin, manager, user)
- Email validation and full name presentation methods
- Import model with status tracking and file attachment
- Dashboard broadcaster concern for real-time updates
- Application record base class and model associations
- Application mailer for email functionality

Author: lucasleandro1

app/mailers/application_mailer.rb

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+class ApplicationMailer < ActionMailer::Base
+  default from: "[email protected]"
+  layout "mailer"
+end

app/models/application_record.rb

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+class ApplicationRecord < ActiveRecord::Base
+  primary_abstract_class
+end

app/models/concerns/.keep

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+module DashboardBroadcaster
+  extend ActiveSupport::Concern
+
+  included do
+    after_commit :broadcast_dashboard_update, on: [ :create, :update, :destroy ]
+  end
+
+  private
+
+  def broadcast_dashboard_update
+    # Broadcast updated statistics to admin dashboard
+    ActionCable.server.broadcast(
+      "dashboard_updates",
+      {
+        type: "stats_update",
+        stats: {
+          total_users: User.total_count,
+          admin_users: User.admin_count,
+          regular_users: User.user_count
+        },
+        timestamp: Time.current.iso8601
+      }
+    )
+  end
+end

app/models/concerns/dashboard_broadcaster.rb

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+class Import < ApplicationRecord
+  belongs_to :user
+  has_one_attached :file
+
+  # Status enum
+  STATUSES = %w[pending processing completed failed].freeze
+  
+  validates :file_name, presence: true
+  validates :status, inclusion: { in: STATUSES }
+  validates :progress, numericality: { greater_than_or_equal_to: 0, less_than_or_equal_to: 100 }
+  
+  scope :recent, -> { order(created_at: :desc) }
+  scope :by_status, ->(status) { where(status: status) if status.present? }
+
+  # Status helpers
+  def pending?
+    status == 'pending'
+  end
+
+  def processing?
+    status == 'processing'
+  end
+
+  def completed?
+    status == 'completed'
+  end
+
+  def failed?
+    status == 'failed'
+  end
+
+  # Progress calculation
+  def calculate_progress
+    return 0 if total_rows.zero?
+    ((processed_rows.to_f / total_rows) * 100).round(2)
+  end
+
+  def update_progress!
+    self.progress = calculate_progress
+    save!
+  end
+
+  # Error handling
+  def add_error(error_message)
+    self.error_details = error_details.to_s + "\n#{Time.current}: #{error_message}"
+    save!
+  end
+
+  def success_rate
+    return 0 if processed_rows.zero?
+    ((successful_rows.to_f / processed_rows) * 100).round(2)
+  end
+
+  # Display helpers
+  def display_status
+    status.humanize
+  end
+
+  def estimated_time_remaining
+    return nil unless processing? && processed_rows > 0
+    
+    elapsed_time = Time.current - updated_at
+    avg_time_per_row = elapsed_time / processed_rows
+    remaining_rows = total_rows - processed_rows
+    
+    (remaining_rows * avg_time_per_row).seconds
+  end
+end

app/models/import.rb

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+class User < ApplicationRecord
+  include DashboardBroadcaster
+
+  # Include default devise modules. Others available are:
+  # :confirmable, :lockable, :timeoutable, :trackable and :omniauthable
+  devise :database_authenticatable, :registerable,
+         :recoverable, :rememberable, :validatable, :trackable
+
+  # Active Storage for avatar image
+  has_one_attached :avatar_image
+
+  # Validations
+  validates :full_name, presence: true, length: { minimum: 2, maximum: 100 }
+  validates :role, presence: true, inclusion: { in: %w[user admin] }
+  validates :avatar_url, format: { with: URI::DEFAULT_PARSER.make_regexp([ "http", "https" ]) }, allow_blank: true
+
+  # Enums
+  enum :role, { user: "user", admin: "admin" }
+
+  # Scopes
+  scope :admins, -> { where(role: "admin") }
+  scope :regular_users, -> { where(role: "user") }
+
+  # Methods
+  def admin?
+    role == "admin"
+  end
+
+  def display_name
+    full_name.presence || email
+  end
+
+  def initials
+    return "??" if full_name.blank?
+
+    full_name.split(" ")
+             .map { |word| word[0]&.upcase }
+             .compact
+             .first(2)
+             .join
+  end
+
+  def avatar
+    if avatar_image.attached?
+      avatar_image
+    elsif avatar_url.present?
+      avatar_url
+    else
+      nil
+    end
+  end
+
+  # Class methods
+  def self.total_count
+    count
+  end
+
+  def self.admin_count
+    admins.count
+  end
+
+  def self.user_count
+    regular_users.count
+  end
+end