fix(manager-core): F-Q-005 preserve AuthzDenied::Repo through service-layer authz checks

Every check_read/check_write/check_publish helper across kv, docs,
files, pubsub, queue services used `.map_err(|_| KvError::Forbidden)?`,
collapsing AuthzDenied::Denied AND AuthzDenied::Repo(repo_err) into
a single Forbidden. A transient Postgres blip during the membership
lookup surfaced as 403 to scripts; operators couldn't distinguish
"real forbidden" from "DB flap during permission check".

Replace each call site with the explicit match pattern already used by
users_service::require (users_service.rs:177-181):

  Ok(())                          → continue
  Err(AuthzDenied::Denied)        → Err(ServiceError::Forbidden)
  Err(AuthzDenied::Repo(e))       → Err(ServiceError::Backend(e.to_string()))

7 call sites updated (2 in kv_service, 2 in docs_service, 2 in
files_service, 2 in pubsub_service, 1 in queue_service).

AUDIT.md anchor: F-Q-005. Depends on F-Q-004 (which added Backend
to QueueError/PubsubError).

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

crates/manager-core/src/queue_service.rs

@@ -59,13 +59,17 @@ impl QueueService for QueueServiceImpl {
         // check (cx.principal is None); authenticated callers must hold
         // AppQueueEnqueue.
         if let Some(principal) = cx.principal.as_ref() {
-            authz::require(
+            match authz::require(
                 &*self.authz,
                 principal,
                 Capability::AppQueueEnqueue(cx.app_id),
             )
             .await
-            .map_err(|_| QueueError::Forbidden)?;
+            {
+                Ok(()) => {}
+                Err(authz::AuthzDenied::Denied) => return Err(QueueError::Forbidden),
+                Err(authz::AuthzDenied::Repo(e)) => return Err(QueueError::Backend(e.to_string())),
+            }
         }
 
         let deliver_after = opts