[FEATURE] In-session keybinding/command to terminate the current session (equivalent of Agents-view Ctrl-X)

Gap. Inside a single agent's chat view, there's no way for the human to kill this session. To terminate it, the human has to leave the chat, navigate to the Agents view, and press Ctrl-X there.

Why it matters. Once you've decided a session is done (result landed, going sideways, no longer needed), the context-switch out to the Agents view just to kill it is friction — especially when the human is already in the chat reading the final output. With many parallel sessions, this turns into a lot of round trips.

Proposed UX. A keybinding from within the chat view (e.g. the same Ctrl-X) that terminates the focused session. Or a slash command like /kill-session. Whatever shape matches existing patterns.