feat(backend): demo scheduler on the virtual clock — doses, missed, check-ins, scales, silence

- app/scheduler/demo.py: run_until(now) replays due and fresh events in time order: dose rows +
  med_reminder, missed after 2 h without an answer → monitoring, daily_checkin, scale_due by the
  config/modules.yaml schedules, daily monitoring pass (silence, missed doses) → reach_out/scale_due
- idempotent via scheduler_events (unique token+key); stale events are not sent; no contact without
  consent or during an open crisis
- config/scheduler.yaml: times and windows; runs while the questionnaire release is off
- POST /demo/clock/advance replays the scheduler up to the new time

Refs #13

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

tests/test_db.py

@@ -70,6 +70,7 @@ async def test_create_all_puts_tables_in_the_right_db(dbs: None) -> None:
         "questionnaire_records",
         "questionnaire_notices",
         "questionnaire_tasks",
+        "scheduler_events",
     } == clinical_tables
     await init_db()  # idempotent