feat(event-subscriber): accept partial_update as a register write (refs #153)

The ACL upserts with PATCH, so every approval notification carries actie `partial_update`.
Accepting it makes the INGEDIEND → INGESCHREVEN transition project. `update` stays accepted
so a PUT-shaped write behaves the same; `destroy` deliberately does not — removing a
registration from the public register is its own decision, not a side effect of this one.

ADR-0030 records why the actie list is what it is.

docs/architecture/adr-0030-projection-sourced-from-the-register.md

@@ -34,6 +34,12 @@ notification points at. The projection is a cache of the register; ZGW is no lon
   as a kenmerk — so the record is read back through the ACL (`POST /register-records/read`).
   §8.1 applies to Objecten exactly as ADR-0028 established: the ACL is the only code that talks
   to it.
+- The accepted acties are `create`, `update` and `partial_update`. The last one is not
+  defensive breadth: the ACL upserts with PATCH, and DRF routes a PATCH through the notifying
+  `update()` while naming the action `partial_update` — which is what Objecten publishes. So
+  every approval arrives as `partial_update`, and accepting only `create`/`update` drops the
+  one state change this slice exists to project. `destroy` is deliberately not accepted:
+  removing a registration from the public register is its own decision.
 - The record already carries `id`, `status` and `reference`, so the row is the record. The
   zaak-shaped surface goes: `IsZaakCreated`, `IsZaakStatusSet`, `ZaakUrl`, `ZaakId`, and
   `ToEntry`'s `Resource == "status"` inference are replaced by `IsRegisterRecordWritten` +

services/event-subscriber/EventSubscriber.Application/Notification.cs

@@ -18,10 +18,20 @@ public sealed record Notification(
     string Actie,
     Uri ResourceUrl)
 {
-    /// <summary>A register record written to Objecten — <c>create</c> on submit, <c>update</c> on
-    /// approval, since the ACL upserts the same object for a registration (§8.6).</summary>
+    /// <summary>
+    /// A register record written to Objecten — <c>create</c> on submit and <c>partial_update</c> on
+    /// approval, since the ACL upserts the same object for a registration (§8.6).
+    /// </summary>
+    /// <remarks>
+    /// <c>partial_update</c> is what a PATCH actually reports: DRF routes it through the notifying
+    /// <c>update()</c> but names the action <c>partial_update</c>, and that is what Objecten puts in
+    /// the notification. <c>update</c> is accepted too, so a PUT-shaped write would project the same
+    /// way. <c>destroy</c> is deliberately not: removing a registration from the public register is
+    /// its own decision, not a side effect of this one.
+    /// </remarks>
     public bool IsRegisterRecordWritten =>
-        Kanaal == "objecten" && Resource == "object" && Actie is "create" or "update";
+        Kanaal == "objecten" && Resource == "object"
+        && Actie is "create" or "update" or "partial_update";
 
     /// <summary>The object holding the register record. For a <c>resource: object</c> notification
     /// Objecten sends the object as both <c>hoofdObject</c> and <c>resourceUrl</c> — the object is