Better management controls for coach check-in and follow-up messages

Add clearer management of automated coach check-in/follow-up messages so users don't get multiple messages dumped when starting a workout. Suggested improvements: queue visibility (show pending vs delivered), deduplication, message expiration (stale prompts auto-cancel), and user controls to snooze/disable specific categories (e.g., cravings check-ins, technique check-ins) or limit to one check-in per session.