[Feature] Add /btw side-question command in Kimi Code

[MengyangGao]

What feature would you like to see?

Legacy kimi-cli supported /btw <question> as a side-question command. In the new TypeScript-based Kimi Code(for now, v0.5.0) implementation, /btw does not appear in the built-in slash command registry or the current slash command documentation, and using it behaves as an unknown slash input / normal message instead of opening a side-question flow.

Legacy behavior

In legacy kimi-cli, /btw allowed the user to ask a quick side question without interrupting the main conversation.

Documented behavior:

• Usage: /btw <question>
• Available both when idle and during streaming.
• Runs in an isolated context.
• Can see conversation history.
• Does not modify the main conversation history.
• Tool calls are disabled; response is text-only.
• During streaming, the response appears in a scrollable modal panel.
• Wire / ACP clients could use BtwBegin / BtwEnd with run_side_question().

Expected behavior

Kimi Code should restore feature parity with legacy kimi-cli:

/btw <question>

Additional information

No response