docs(acl): ADR-0019 + demo/backlog for zaak cancellation on timeout (S-10c) (refs #106)

Records the ZGW cancellation-modelling decision (distinct non-terminal
Geannuleerd status + Vervallen resultaat, resolved by name) and documents the
end-to-end timeout-cancellation path.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

BACKLOG.md

@@ -215,7 +215,9 @@ Split (issue #11 closed) into two independently-demoable slices per §13 — the
 
 #### S-10c · Close the ZGW zaak on document-timeout expiry — #106
 
-**Outcome:** when the 30-day term lapses (S-10a `RegistratieVerlopen`), the ZGW zaak is set to a cancellation status (not just the domain aggregate → `Verlopen`). Adds a cancellation statustype/resultaattype to the seed + an ACL method + expiry-worker wiring. Carved from S-10b (ADR-0017/0018). Depends on #103.
+**Outcome:** when the 30-day term lapses (S-10a `RegistratieVerlopen`), the ZGW zaak is set to a distinct non-terminal `Geannuleerd` status + `Vervallen` resultaat (not just the domain aggregate → `Verlopen`), resolved by name in the ACL. Adds the cancellation statustype/resultaattype to the seed + an ACL `CancelZaakAsync`/`POST /annuleringen` + expiry-worker wiring. Carved from S-10b (ADR-0017/0018/0019). Depends on #103.
+
+**Acceptance:** ACL↔OpenZaak integration test (cancellation records `Geannuleerd` + a resultaat, live); the domain verify script fires the P30D timer and asserts the zaak reaches `Geannuleerd` end-to-end; BDD asserts the zaak is cancelled on timeout but untouched when documents arrive in time.
 
 ### S-11 · Withdrawal (Flow 3)