Add require_categories DSL option and fix ActiveSupport dependency

- Add `require_categories true` DSL macro: when set, multi-label
  classifiers return Result.failure when no valid categories are found
  (previously multi-label always returned success with empty array)
- Fix .blank? call in Web content fetcher's normalize_redirect_url
  that required ActiveSupport. Replaced with nil/empty check.
- Bump version to 0.2.0

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: DmitrySychev

lib/llm_classifier/classifier.rb

@@ -7,7 +7,8 @@ module LlmClassifier
   class Classifier
     class << self
       attr_reader :defined_categories, :defined_system_prompt, :defined_model,
-                  :defined_adapter, :defined_multi_label, :defined_knowledge,
+                  :defined_adapter, :defined_multi_label, :defined_require_categories,
+                  :defined_knowledge,
                   :before_classify_callbacks, :after_classify_callbacks
 
       def categories(*cats)
@@ -50,6 +51,14 @@ def multi_label(value = nil)
         end
       end
 
+      def require_categories(value = nil)
+        if value.nil?
+          @defined_require_categories || false
+        else
+          @defined_require_categories = value
+        end
+      end
+
       def knowledge(&)
         if block_given?
           @defined_knowledge = Knowledge.new
@@ -192,7 +201,10 @@ def extract_valid_categories(json)
     end
 
     def should_fail?(valid_categories)
-      valid_categories.empty? && !self.class.categories.empty? && !self.class.multi_label
+      return false if valid_categories.any?
+      return false if self.class.categories.empty?
+
+      !self.class.multi_label || self.class.require_categories
     end
 
     def build_failure_result(response, json)

lib/llm_classifier/content_fetchers/web.rb

@@ -77,7 +77,7 @@ def private_ip?(address)
       end
 
       def normalize_redirect_url(base_url, redirect_url)
-        return nil if redirect_url.blank?
+        return nil if redirect_url.nil? || redirect_url.empty?
 
         if redirect_url.start_with?("http://", "https://")
           redirect_url

lib/llm_classifier/version.rb

@@ -1,5 +1,5 @@
 # frozen_string_literal: true
 
 module LlmClassifier
-  VERSION = "0.1.0"
+  VERSION = "0.2.0"
 end