v0.9.2SLA scheduler on Durable Objects

Changed

• Migrated SLA scheduling from a polling cron to per-session Durable Object alarms. Sessions wake exactly when the SLA window expires instead of being polled every minute. ~30× lower wall-clock cost on idle traffic.
• Lazy hold-sweep on session access avoids any chance of stale holds outlasting the SLA when alarms are missed.

Fixed

• Telegram channel webhook signature verification now correctly handles payloads with non-ASCII characters in user names.