seamless sessions command (list and revoke)

[Bccorb]

Summary

List and revoke the authenticated user's active sessions from the terminal.

Tasks

• seamless sessions [list]: GET /sessions. Render id, device or user agent, IP, created and last-used timestamps, and a current-session marker.
• seamless sessions revoke <id>: DELETE /sessions/:id.
• seamless sessions revoke --all: DELETE /sessions.
• Confirm before revoking the current session.

Acceptance criteria

• Listing shows all active sessions for the user.
• Revoking a session is reflected on the next list.
• Revoking the current session prompts for confirmation first.

Part of #38