refactor(ai): 优化 AI 提示词构建逻辑

- withLanguagePreferencePrompt: 修复无语言标签时占位符未添加的问题
- handleBeforeSend: 简化操作会话提示词，移除冗余的工具名称说明

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

resources/assets/js/components/AIAssistant/float-button.vue

@@ -405,7 +405,7 @@ export default {
             // 添加操作会话信息
             let operationContext = '';
             if (this.operationSessionId) {
-                operationContext = `\n\n前端操作会话已建立，session_id: ${this.operationSessionId}。你可以使用 get_page_context、execute_action、execute_element_action 工具直接操作用户的页面。`;
+                operationContext = `\n\n页面操作会话 session_id: ${this.operationSessionId}。`;
             }
 
             const prepared = [

resources/assets/js/utils/ai.js

@@ -360,10 +360,8 @@ const withLanguagePreferencePrompt = (prompt) => {
         return prompt;
     }
     const label = languageList[languageName] || languageName || '';
-    if (!label) {
-        return prompt;
-    }
-    return `${prompt}\n\n${LANGUAGE_PREFERENCE_PROMPT(label)}\n\n${SYSTEM_OPTIONAL_PROMPTS_PLACEHOLDER}`;
+    const languagePart = label ? `\n\n${LANGUAGE_PREFERENCE_PROMPT(label)}` : '';
+    return `${prompt}${languagePart}\n\n${SYSTEM_OPTIONAL_PROMPTS_PLACEHOLDER}`;
 };
 
 /**