Allow Claude to set the session name and color

Problem

Claude can observe the session name (it arrives as a system-reminder after /rename) but cannot set it. Same for /color. Both are user-only meta-commands intercepted by the CLI before reaching the model.

This forces the user to manually label every session, even when Claude has better information about the session's actual focus — especially in long sessions, /loop runs, and scheduled remote agents where no human is at the keyboard to rename.

Acceptance criteria

Claude should be able to:

1. Set the current session's name to an arbitrary string.
2. Set the current session's color to one of the supported values.
3. Read back the current name and color (already partially true for name via system-reminder).

Out of scope (explicitly): any meta-command with side effects on context, config, auth, or process lifecycle (/clear, /compact, /config, /exit, /login, etc.).

Use cases

• Autonomous /loop and scheduled-agent runs self-label by detected focus instead of staying as the default name.
• Long sessions rename themselves when topic shifts ("debugging X" → "shipping X").
• Color-coding by repo / branch / task type without user intervention.

Notes

Implementation is open — a dedicated tool, a whitelisted Skill-style invocation, or anything else that satisfies the criteria above. The point is the capability, not the mechanism.