Add skip_email_confirmation option; fix SQLite length validation

Introduce config.skip_email_confirmation in application.rb.dist.
When set to true, new registrations are automatically confirmed
without requiring email verification — useful for installations
where outgoing email is not configured or for development/testing.
Implemented by calling skip_confirmation! in build_resource before
the record is saved, so no confirmation email is ever sent.

Also fix ArgumentError raised in length validations when
type_for_attribute(:column).limit returns nil, which happens with
SQLite for string columns that have no explicit limit in the
migration. Guard with || Float::INFINITY so the validation is
effectively skipped when the database imposes no limit.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

app/controllers/registrations_controller.rb

@@ -8,6 +8,14 @@ class RegistrationsController < Devise::RegistrationsController
 
   protected
 
+  def build_resource(hash = {})
+    super
+    # Skip the email confirmation step when the admin has opted out of it via
+    # config.skip_email_confirmation in application.rb.  The account becomes
+    # active immediately so the user can sign in right after registering.
+    resource.skip_confirmation! if Rails.application.config.skip_email_confirmation
+  end
+
   def update_resource(resource, params)
     # Based on update_with_password()
     if params[:password].blank?