When user selects "dedicated bot number" mode (selfChatMode=false),
skip the dmPolicy question and default to allowlist. Prompt for
allowed phone numbers immediately.
This is simpler and safer than pairing mode, which sends codes to
whoever messages the bot.
Users who want pairing or open mode can edit lettabot.yaml manually.
Also updates docs to reflect the new defaults.
Written by Cameron ◯ Letta Code
"Simplicity is the ultimate sophistication." - Leonardo da Vinci
