feat(setup): paint "assistant" green in the agent-name prompt

Wraps the word "assistant" in `accentGreen` (#3fba50, added in #2103)
across the six channel adapters that ask "What should your assistant
be called?" — Discord, iMessage, Signal, Slack, Telegram, WhatsApp.
Mirrors the green emphasis on "you" in the display-name prompt: the
green word names the subject of the question (assistant vs operator)
so the operator parses it at a glance.

setup/channels/imessage.ts

@@ -36,7 +36,7 @@ import * as setupLog from '../logs.js';
 import { brightSelect } from '../lib/bright-select.js';
 import { askOperatorRole } from '../lib/role-prompt.js';
 import { ensureAnswer, fail, runQuietChild } from '../lib/runner.js';
-import { note, wrapForGutter } from '../lib/theme.js';
+import { accentGreen, note, wrapForGutter } from '../lib/theme.js';
 
 const DEFAULT_AGENT_NAME = 'Nano';
 
@@ -303,7 +303,7 @@ async function resolveAgentName(): Promise<string> {
   }
   const answer = ensureAnswer(
     await p.text({
-      message: 'What should your assistant be called?',
+      message: `What should your ${accentGreen('assistant')} be called?`,
       placeholder: DEFAULT_AGENT_NAME,
       defaultValue: DEFAULT_AGENT_NAME,
     }),