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.Tests/InMemoryRegistrationStoreTests.cs

@@ -79,7 +79,7 @@ public class InMemoryRegistrationStoreTests
         switch (transition)
         {
             case nameof(Registration.Withdraw): registration.Withdraw(); break;
-            case nameof(Registration.Approve): registration.Approve(); break;
+            case nameof(Registration.Approve): registration.Approve(DateTimeOffset.UtcNow); break;
             case nameof(Registration.Reject): registration.Reject(); break;
             case nameof(Registration.Expire): registration.Expire(); break;
         }
@@ -96,4 +96,27 @@ public class InMemoryRegistrationStoreTests
 
         Assert.Null(await store.FindOpenByBsnAsync("123456782"));
     }
+
+    [Fact]
+    public async Task Finds_only_the_inscriptions_due_for_a_herregistratie_reminder()
+    {
+        var now = new DateTimeOffset(2026, 7, 23, 0, 0, 0, TimeSpan.Zero);
+        var store = new InMemoryRegistrationStore();
+
+        var due = Registration.Submit("123456782");
+        due.AttachZaak(new Uri("http://openzaak/zaken/api/v1/zaken/abc"));
+        due.Approve(now - Registration.HerregistratieGeldigheid + Registration.Herinneringstermijn);
+        await store.SaveAsync(due);
+
+        var freshlyInscribed = Registration.Submit("111111110");
+        freshlyInscribed.AttachZaak(new Uri("http://openzaak/zaken/api/v1/zaken/def"));
+        freshlyInscribed.Approve(now);
+        await store.SaveAsync(freshlyInscribed);
+
+        await store.SaveAsync(Registration.Submit("222222222")); // still INGEDIEND — never inscribed
+
+        var result = await store.FindDueForHerregistratieReminderAsync(now);
+
+        Assert.Equal([due.Id], result.Select(r => r.Id).ToArray());
+    }
 }