Verify and fix daily PR summary cron wiring

Confirm a scheduled session or cron runs /home/agent/agents/slava-agent/bin/generate-pr-summary.sh at 07:00 UTC (09:00 Warsaw). If missing, create the schedule. If present, verify it gates on check-dm-quiet.sh/check-dm-mute.sh, suppresses when output is empty, sends via the message tool, and records the DM via record-dm.sh. Also confirm ~/.dm-quiet-until reset logic is tied to successful sends or a bounded expiry.