feat: ✨ Create users

Users migration, model, controller. user_id to links. signup view

app/controllers/users_controller.rb

@@ -0,0 +1,23 @@
+# frozen_string_literal: true
+
+class UsersController < ApplicationController
+  def new
+    @user = User.new
+  end
+
+  def create
+    @user = User.create(user_params)
+    if @user.errors.any?
+      render json: @user.errors, status: :unprocessable_entity
+    else
+      session[:user_id] = @user.id
+      redirect_to '/'
+    end
+  end
+
+  private
+
+  def user_params
+    params.require(:user).permit(:username, :password)
+  end
+end