feat(domain): herregistratie reminder sweep on a Quartz cron (S-17, closes #18) (#121)

## What & why

S-17: a BIG inscription is valid for a fixed term; before it lapses the zorgprofessional must herregistreren. This adds a **daily herregistratie reminder sweep**.

- **Domain:** `Approve(ingeschrevenOp)` now stamps the inscription moment; `HerregistratieVoor` derives the deadline (inscription + 5-year validity); `HerregistratieReminderDue(asOf)` is the single rule (inside the 90-day window, inscribed, not yet reminded); `MarkHerregistratieReminderVerstuurd()` is idempotent.
- **Store:** `FindDueForHerregistratieReminderAsync(asOf)` — the sweep's candidate set, filtered on the aggregate's own rule (no duplicated policy).
- **Application:** `HerregistratieReminderSweep` — pure over the store + an injected `TimeProvider`; flags + persists each due inscription, returns the reminded ids.
- **Infra/API:** `HerregistratieReminderJob` (Quartz `IJob`) fires the sweep on a daily cron (03:00, overridable via `Quartz__Cron`) and logs the count. `GET /registrations/{id}` surfaces `herregistratieVoor` + `herregistratieReminderVerstuurd`.

**Decisions (both raised with you before coding):** use Quartz.NET as the PRD names it — a genuine cron concern, distinct from the queue-draining pumps, which stay as-is (**ADR-0022**, proposal #120); and the reminder's observable effect is a flag on the aggregate + a log line (no outbound notification infra in v1). No coupling rule (§8) is touched — Quartz is internal to the Domain Service.

Closes #18
Closes #120

## Definition of Done

- [x] Linked Gitea issue (above).
- [x] Failing test committed before the implementation (red→green per layer: domain rule, store query, sweep).
- [x] Implementation makes the test pass; refactor commit for the 90-day knob.
- [x] Conventional Commits referencing the issue (`refs #18`).
- [ ] CI green — awaiting Gitea Actions.
- [ ] `docker compose up` reaches green health checks within 3 minutes — API boots locally with Quartz initialised; verified in CI compose smoke.
- [x] Docs updated — ADR-0022, demo-script, BACKLOG.
- [x] ADR added — `docs/architecture/adr-0022-quartz-scheduler.md`.
- [x] Demo note in `docs/demo-script.md`.

## Notes for reviewers

- **Ripple:** `Approve()` gained the inscription moment, so the two approving handlers (`ApproveRegistration`, `BeoordeelRegistratie`) now take an injected `TimeProvider`; existing tests pass a fixed clock. All three `IRegistrationStore` implementers (prod, unit fake, acceptance) got the new query.
- **Calibration knobs:** validity (5y) and reminder lead time (90d) are domain constants marked with `ponytail:` comments; promotion path to beheer config (S-15) noted in the ADR.
- **Mutation:** the Quartz job shell is excluded from Stryker, mirroring the pumps; all rule/sweep/query logic is covered.
- Local: 152 domain unit tests green; API boots with the Quartz scheduler and `/health` green.

Reviewed-on: #121

services/domain/Big.Infrastructure/InMemoryRegistrationStore.cs

@@ -26,4 +26,9 @@ public sealed class InMemoryRegistrationStore : IRegistrationStore
     public Task<Registration?> FindOpenByBsnAsync(string bsn, CancellationToken ct = default)
         => Task.FromResult(_byId.Values.FirstOrDefault(r =>
             r.Bsn == bsn && r.Status is RegistrationStatus.Ingediend or RegistrationStatus.InBehandeling));
+
+    public Task<IReadOnlyList<Registration>> FindDueForHerregistratieReminderAsync(
+        DateTimeOffset asOf, CancellationToken ct = default)
+        => Task.FromResult<IReadOnlyList<Registration>>(
+            _byId.Values.Where(r => r.HerregistratieReminderDue(asOf)).ToList());
 }