Diagnose and fix Slack DM channel_not_found for Slava

The Slack DM to Slava (stored channel D0AUBPV0FM0) has failed with channel_not_found for multiple days, blocking all outbound DMs. Investigate: check check-dm-quiet.sh/check-dm-mute.sh/record-dm.sh configuration, verify the stored channel ID and bot token permissions, and either fix the channel ID or escalate to Victor. Do not schedule another DM to Slava until this is resolved.