fix: ensure StreamMemory.search matches added docs (Fixes #59)

[februarysea]

概要
修复了 StreamMemory.search 方法始终返回空结果的问题。

解决方案
在 add 方法中补充 "type": "stream" 标签，使 search 方法能够正确匹配并返回已存储的记忆。

复现结果对比
修复前：

2025-08-30 20:15:14,186 - Agent - INFO - agent1 search memories: Nothing
2025-08-30 20:15:14,186 - Agent - INFO - agent1 all memories: [{'id': 0, 'cognition_id': None, 'topic': 'Event', 'location': 500030808, 'description': 'I ate with my friend', 'day': 0, 't': 28801}, {'id': 1, 'cognition_id': None, 'topic': 'Event', 'location': 500030808, 'description': 'I met my friend', 'day': 0, 't': 28801}, {'id': 2, 'cognition_id': None, 'topic': 'Event', 'location': 500030808, 'description': 'I talked with my friend', 'day': 0, 't': 28801}, {'id': 3, 'cognition_id': None, 'topic': 'Event', 'location': 500030808, 'description': 'I met another friend', 'day': 0, 't': 28801}, {'id': 4, 'cognition_id': None, 'topic': 'Event', 'location': 500030808, 'description': 'I ate with another friend', 'day': 0, 't': 28801}]

修复后：

2025-08-30 20:21:57,207 - Agent - INFO - agent1 search memories: 
- [Event]: I talked with my friend [day: 0, time: 08:00:01, location: unknown]
- [Event]: I met my friend [day: 0, time: 08:00:01, location: unknown]
- [Event]: I ate with my friend [day: 0, time: 08:00:01, location: unknown]
- [Event]: I ate with another friend [day: 0, time: 08:00:01, location: unknown]
- [Event]: I met another friend [day: 0, time: 08:00:01, location: unknown]
2025-08-30 20:21:57,207 - Agent - INFO - agent1 all memories: [{'id': 0, 'cognition_id': None, 'topic': 'Event', 'location': 500024168, 'description': 'I ate with my friend', 'day': 0, 't': 28801}, {'id': 1, 'cognition_id': None, 'topic': 'Event', 'location': 500024168, 'description': 'I met my friend', 'day': 0, 't': 28801}, {'id': 2, 'cognition_id': None, 'topic': 'Event', 'location': 500024168, 'description': 'I talked with my friend', 'day': 0, 't': 28801}, {'id': 3, 'cognition_id': None, 'topic': 'Event', 'location': 500024168, 'description': 'I met another friend', 'day': 0, 't': 28801}, {'id': 4, 'cognition_id': None, 'topic': 'Event', 'location': 500024168, 'description': 'I ate with another friend', 'day': 0, 't': 28801}]

关联 Issue
#59