feat: Add AI credit topup flow for Stripe (#12988)

Co-authored-by: Shivam Mishra <scm.mymail@gmail.com>
Co-authored-by: Pranav <pranav@chatwoot.com>

enterprise/app/controllers/enterprise/api/v1/accounts_controller.rb

@@ -55,6 +55,17 @@ class Enterprise::Api::V1::AccountsController < Api::BaseController
     end
   end
 
+  def topup_checkout
+    return render json: { error: I18n.t('errors.topup.credits_required') }, status: :unprocessable_entity if params[:credits].blank?
+
+    service = Enterprise::Billing::TopupCheckoutService.new(account: @account)
+    redirect_url = service.create_checkout_session(credits: params[:credits].to_i)
+    render json: { redirect_url: redirect_url }
+  rescue Enterprise::Billing::TopupCheckoutService::Error => e
+    Rails.logger.error("Topup checkout failed for account #{@account.id}: #{e.message}")
+    render_could_not_create_error(e.message)
+  end
+
   private
 
   def check_cloud_env