[Feature Request] Add /nuke command to delete client and server session copies on key compromise

**Bug Description**
i'd like a /nuke command that will delete both client and server copies of a session (and restart the current session) for use in situations like key leaks into sessions. claude has accidently read private keys due to script errors many times. I'd feel better about this if i could know that i have killed all the session data that has the key in it. Even if i roll the key being able to remove any copy of it is good policy.

**Environment Info**
- Platform: darwin
- Terminal: vscode
- Version: 2.1.263
- Feedback ID: b578d4fd-6f09-40b8-8d99-2a15d5d48fbe

Start by finding how Claude Code handles slash commands and where client and server session data are stored. The requested outcome is a /nuke command that deletes both copies of the current session and restarts it after possible key compromise. This likely needs maintainer guidance on server-side deletion semantics and safety before implementation.

索引モデルが issue の本文から書いたものです。