Refactor serialization methods to use to_h instead of as_json for attachments

Author: crmne

lib/ruby_llm/attachment.rb

@@ -78,7 +78,7 @@ def text?
       RubyLLM::MimeType.text? mime_type
     end
 
-    def as_json
+    def to_h
       { type: a.type, source: a.source }
     end
 

lib/ruby_llm/content.rb

@@ -28,8 +28,8 @@ def format
     end
 
     # For Rails serialization
-    def as_json
-      { text: @text, attachments: @attachments.map(&:as_json) }
+    def to_h
+      { text: @text, attachments: @attachments.map(&:to_h) }
     end
 
     private