Restore quick delete action in the sessions view

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

The sessions list used to support deleting a session directly from the list (a quick delete/keyboard action on the highlighted row). That option is gone, and there is now no good way to delete sessions.

### Proposed solution

• Re-add a delete action in the sessions view that operates on the highlighted session without opening it (e.g.  d  or  Del  key, with a confirmation prompt).
• Support deleting multiple sessions in one pass (multi-select, or stay in the list after each delete).
• Deleting from the list should not create a new session; the user should remain in the sessions view with the deleted entry removed.

### Example prompts or workflows

_No response_

### Additional context

The only remaining path is  /session delete , which has two significant problems:

1. It requires opening a session first. You must resume/enter a session before you can delete it, so cleaning up several stale sessions means repeatedly opening sessions you have no interest in.
2. It spawns a replacement session. After deleting, the CLI immediately creates a brand-new session. So deleting N sessions leaves you with N new empty sessions to clean up, which is extremely frustrating.

先追蹤工作階段檢視畫面和現有的 `/session delete` 命令，特別確認醒目顯示的列、鍵盤操作、確認以及工作階段建立是如何處理的。先驗證目前的刪除流程。完成的條件是從清單中刪除一個或多個醒目顯示的工作階段，不開啟它們或建立替代工作階段，並讓使用者留在工作階段檢視畫面中。

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