[FEATURE] Ability to send /theme mid-turn

Preflight Checklist

• [x] I have searched existing requests and this feature hasn't been requested yet
• [x] This is a single feature request (not multiple features)

Problem Statement

Currently, it is impossible to change your theme in the Claude Code harness while Claude is mid-turn. It gets queued and you have to wait for the turn to finish.

Proposed Solution

You should be able to simply do it whenever, there's absolutely no reason this needs to be dependent on agent turns at all, it's purely a harness setting.

Alternative Solutions

_No response_

Priority

Low - Nice to have

Feature Category

Interactive mode (TUI)

Use Case Example

_No response_

Additional Context

_No response_