setup: drop "E.164" jargon from iMessage handle card

Replace "full E.164, e.g. +15551234567" with plain-language guidance
mirroring the WhatsApp setup card: "start with + and your country code,
no spaces or dashes" plus a worked example. "E.164" is the technical
name for the format and means nothing to non-telecom users; the
explanation it stands in for is one sentence.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

setup/channels/imessage.ts

@@ -290,7 +290,8 @@ async function askOperatorHandle(): Promise<string> {
       "What phone number or email do you iMessage with?",
       "That's where your assistant will send its welcome message.",
       '',
-      k.dim('  • Phone: full E.164, e.g. +15551234567'),
+      k.dim('  • Phone: start with + and your country code, no spaces or dashes'),
+      k.dim('    Example: +14155551234 (country code 1, then 4155551234)'),
       k.dim('  • Email: whatever iMessage recognises (Apple ID, iCloud alias, …)'),
     ].join('\n'),
     'Your iMessage handle',