fix: 修复19个Bug (P0-P3) — 持续性调试第7轮发现的问题

P0 (5): crypto/rand session ID, TTS fallback可达性, goroutine defer recover, adminAuth前缀修正
P1 (5): 普通用户密码验证, context传递, priority clamp, 超时重试, 自主思考速率限制
P2 (4): Briefing AI降级, 前端消息类型渲染, Docker Compose补全, PWA 192图标
P3 (5): goroutine错误处理, .gitignore完善, reminder created_at, voice Dockerfile, Go版本更新

backend/gateway/internal/store/reminder_store.go

@@ -71,10 +71,13 @@ func (s *ReminderStore) migrate() error {
 
 // CreateReminder 创建新提醒
 func (s *ReminderStore) CreateReminder(r *Reminder) error {
+	if r.CreatedAt.IsZero() {
+		r.CreatedAt = time.Now()
+	}
 	_, err := s.db.Exec(
-		`INSERT INTO reminders (id, user_id, title, description, remind_at, status, repeat_type, session_id)
-		 VALUES ($1, $2, $3, $4, $5, $6, $7, $8)`,
-		r.ID, r.UserID, r.Title, r.Description, r.RemindAt, r.Status, r.RepeatType, r.SessionID,
+		`INSERT INTO reminders (id, user_id, title, description, remind_at, status, created_at, repeat_type, session_id)
+		 VALUES ($1, $2, $3, $4, $5, $6, $7, $8, $9)`,
+		r.ID, r.UserID, r.Title, r.Description, r.RemindAt, r.Status, r.CreatedAt, r.RepeatType, r.SessionID,
 	)
 	if err != nil {
 		return fmt.Errorf("创建提醒失败: %w", err)