调整多模态支持

backend-java/src/main/java/com/pharmacopoeia/service/PromptService.java

@@ -209,9 +209,9 @@ public class PromptService {
                     + "【用户问题】" + query;
         }
 
-        return List.of(
-                Map.of("role", "system", "content", systemPrompt),
-                Map.of("role", "user", "content", userMessage)
-        );
+        List<Map<String, String>> messages = new java.util.ArrayList<>(2);
+        messages.add(new java.util.HashMap<>(Map.of("role", "system", "content", systemPrompt)));
+        messages.add(new java.util.HashMap<>(Map.of("role", "user", "content", userMessage)));
+        return messages;
     }
 }