feat(audit): record the allow path, not just the denial (RB-07)

All five authorization gates audited only their deny branch, so /beheer/audit
could answer "who was turned away" but never "who changed this" — for a
register whose integrity is the product, the wrong half. Nothing recorded the
flag toggle, either org-template write, the admin case or upload delete, the
three brief transitions, or the besluit; the comment claiming endpoints log
their own effect held for two of the eight.

Each gate now computes the decision once, audits it, and then acts. The row
is written by the gate rather than the endpoint, so a new admin endpoint
cannot be added that forgets to audit itself. Same reasoning for the brief:
every transition already funnelled through LogBrief for its log line, so the
audit row goes there too — submit/approve/reject/send in one place, with the
transition's own outcome as the decision, so a 403 or 409 is as visible as a
success.

FlagsAdmin gained a per-call resource, the one deviation from BIO-007's
minimal remediation: the toggle endpoint writes no log line of its own, so a
constant "feature-flags" row would say a flag changed without saying which.
It now records feature-flags/<key>=<value>. OrgAdmin and CasesAdmin keep
coarse refs because those endpoints do log the specific object.

The besluit gets a second row: the gate records that a behandelaar was
allowed to act, aanvraag:besluit records what they decided.

Row volume goes up — StamdataAdmin gates read endpoints, so admin page loads
now write rows. That is what auditing the allow path means; it is also what
would make retention on AuthzAuditStore necessary later.

Closes CQ-004's outstanding half and unblocks signing ADR-C-009.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

backend/tests/BigRegister.Tests/BriefEndpointTests.cs

@@ -160,6 +160,11 @@ public class BriefEndpointTests(TestWebApplicationFactory factory) : IClassFixtu
     var submitted = await res.Content.ReadFromJsonAsync<BriefViewDto>();
     Assert.NotNull(submitted);
     Assert.Equal("submitted", submitted.Brief.Status.Tag);
+
+    // RB-07/BIO-007: the allow side of the transition leaves a row, not just a log line.
+    // Resource is the bare "brief" — never the owner's BSN (RB-02).
+    Assert.Contains(AuthzAuditStore.List(),
+        e => e.Action == "brief:submit" && e.Decision == "allow" && e.Resource == "brief");
   }
 
   [Fact]