[Feature Request] Add mid-session agent switching with /agent command

Bug Description
I want to be able to switch agent team lead mid-session. If I boot claude --agent blah-agent, I want to be able to write /agent foo-agent and get the foo-agent.

Environment Info

• Platform: darwin
• Terminal: Apple_Terminal
• Version: 2.1.114
• Feedback ID: 145a0ba8-61f7-461b-89ce-03c0771db0a9

Errors

[{"error":"Error: Request was aborted.\n    at makeRequest (/$bunfs/root/src/entrypoints/cli.js:50:3448)\n    at processTicksAndRejections (native:7:39)","timestamp":"2026-04-18T20:01:18.952Z"}]