[Feature]: 记忆隔离能力

当前记忆模式按日期生成，所有会话记忆一并被检索，可以参考主流应用引入项目概念，项目本身就是不同处理任务的隔离，项目间记忆也保持隔离，缩小记忆检索范围，提高记忆效果。

The issue names no files, tests, or entry points. Start by locating the date-based memory generation and retrieval flow, then clarify how projects are created, selected, persisted, and isolated. Done should include a defined project model, separated retrieval across projects, and tests proving memories from one project are not returned in another.

Vom Indexierungsmodell aus dem Issue-Text verfasst.