fix: 移除早间简报功能 + 修复多处"人机感"用语

- 删除 briefing_handler.go / briefing_store.go 及所有相关路由与配置
- 移除 Gateway Config 中 ToolEngineURL / BriefingTime 字段
- 移除 DevTools 中 gateway 的 TOOL_ENGINE_URL 环境变量
- webhook 错误提示从"AI 服务异常/暂不可用"改为昔涟自然口吻
- markdown 导出中昔涟头像从 🤖 改为 💫
- 后台思考提示词"系统会误解析"改为"我会误解析"

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

backend/gateway/cmd/main.go

@@ -40,7 +40,6 @@ func main() {
     // 初始化数据库持久化存储 (降级：连接失败不崩溃)
     var sessionStore *store.SessionStore
     var reminderStore *store.ReminderStore
-    var briefingStore *store.BriefingStore
     var automationStore *store.AutomationStore
     var fileStore *store.FileStore
     var knowledgeStore *store.KnowledgeStore
@@ -103,13 +102,6 @@ func main() {
     		logger.Println("✅ 提醒持久化存储已启用 (PostgreSQL)")
     	}
     
-    	// 初始化简报存储（复用同一数据库连接）
-    	if bs, err := store.NewBriefingStore(s.DB()); err != nil {
-    		logger.Printf("⚠ 简报存储初始化失败: %v", err)
-    	} else {
-    		briefingStore = bs
-    		logger.Println("✅ 简报持久化存储已启用 (PostgreSQL)")
-    	}
 
     	// 初始化自动化存储（复用同一数据库连接）
     	if as, err := store.NewAutomationStore(s.DB()); err != nil {
@@ -194,19 +186,13 @@ func main() {
     	logger.Println("[INFO] 思考调度配置文件已加载 (thinking_schedule.json)")
     }
 
-    router.Setup(r, hub, cfg, sessionStore, reminderStore, briefingStore, automationStore, fileStore, ruleEngine, knowledgeStore, nil, db, modelConfigStore, thinkingScheduleStore)
+    router.Setup(r, hub, cfg, sessionStore, reminderStore, automationStore, fileStore, ruleEngine, knowledgeStore, nil, db, modelConfigStore, thinkingScheduleStore)
 
     // 启动提醒调度器
     if reminderStore != nil {
     	handler.StartReminderScheduler(reminderStore, hub)
     }
    
-    // 启动简报调度器
-    if briefingStore != nil && reminderStore != nil {
-    	briefingHandler := handler.NewBriefingHandler(cfg, hub, briefingStore, reminderStore)
-    	handler.StartBriefingScheduler(briefingHandler, briefingStore, cfg.BriefingTime)
-    }
-   
     // 启动服务
     srv := &http.Server{
         Addr:    ":" + cfg.Port,