Add queue expansion to internal/mail/router.go following the expandList() pattern: - Add ErrUnknownQueue error for unknown queue names - Add expandQueue() method to look up QueueConfig from messaging.json - Add TestExpandQueue and TestExpandQueueNoTownRoot tests 🤖 Generated with [Claude Code](https://claude.com/claude-code) Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>