fix(#12): 实现 refresh token 查找功能

- 完善 _find_session_by_refresh_token() 方法
- 使用 session_store.get_session_by_refresh_token() 直接查询
- 利用 Redis 反向索引实现 O(1) 查找复杂度

packages/application/auth/login_use_case.py

@@ -248,20 +248,16 @@ class RefreshTokenUseCase:
         """
         通过 refresh_token 查找 session
         
-        遍历所有 session 查找匹配的 refresh_token（生产环境应使用索引优化）
+        使用 Redis 中的反向索引 (refresh_token -> session_id) 快速查找 session。
+        反向索引在 save_session 时创建，确保了 O(1) 的查找复杂度。
+        
+        Args:
+            refresh_token: 刷新令牌
+            
+        Returns:
+            Session 数据字典，包含 session_id, user_id 等信息；如果不存在返回 None
         """
-        # Scan Redis for all session keys and check refresh_token
-        # This is a simplified implementation - in production, use a reverse index
-        # e.g., store refresh_token -> session_id mapping in Redis
-        
-        # For now, iterate through user sessions
-        # In a real implementation, you would maintain a reverse index:
-        # refresh_token:session_id -> session_id
-        # or use Redis SCAN to find sessions with matching refresh_token
-        
-        # Simplified: iterate users (not scalable for production)
-        # In production, add: session_store.save_refresh_token_index(refresh_token, session_id)
-        return None  # Placeholder - implement with reverse index in production
+        return self.session_store.get_session_by_refresh_token(refresh_token)
 
 
 class LogoutRequest: