Use explicit multiple: keyword in field#select

Cleaner than extracting from attributes hash.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

Author: nimmolo

lib/superform/rails/field.rb

@@ -45,10 +45,7 @@ def textarea(**attributes)
         Components::Textarea.new(field, attributes:)
       end
 
-      def select(*options, **attributes, &)
-        # Extract select-specific parameters from attributes
-        multiple = attributes.delete(:multiple) || false
-
+      def select(*options, multiple: false, **attributes, &)
         Components::Select.new(
           field,
           attributes:,