Track last time a session was open in the session_store

### Describe the feature or problem you'd like to solve

Computer restarts and I need to restore my sessions. Love to review the sessions that were open to recover them.

### Proposed solution

Add a last_open column of type time to session store. Every 5 minutes, update the time in the column. Then I can see when each session was open regardless of whether I took any action in it.

### Example prompts or workflows

show me all the sessions that were open today
show me all the sessions that were open last week
look at all the open sessions from today - is any of them related to feature X?

### Additional context

_No response_

該 issue 提到了 session_store，但沒有提供檔案或測試路徑。先定位該 store 和 session 生命週期的進入點，然後檢查重新啟動後 session 的持久化和查詢方式。完成標準是定期記錄上次開啟時間，並透過測試支援所述的今天和上週 session 工作流程。

由索引模型根據 Issue 內容生成。