Replace in-memory-only setTimeout scheduling with a DB-backed system
that survives broker restarts. Adds:
- `scheduled_message` table in mesh schema (Drizzle + raw CREATE TABLE
for zero-downtime deploys)
- Minimal 5-field cron parser (no dependencies) with next-fire-time
calculation for recurring entries
- On broker boot, all non-cancelled entries are loaded from PostgreSQL
and timers re-armed automatically
- CLI `schedule_reminder` MCP tool accepts optional `cron` expression
- CLI `remind` command accepts `--cron` flag
- One-shot reminders remain backward compatible — no cron field = same
behavior as before
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
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