fix(tests): wire settings registry into the test auth handler — unstick TestAdminCreateUser

setupTestServer built the settings registry (and wired it into
systemSettingsHandler) but never called authHandler.SetSettings, unlike
main.go:112. The auth handler therefore ran with a nil registry and
defaultTimezone() took its nil-fallback branch, returning "UTC" for every
Register/AdminCreateUser in tests regardless of the system default_timezone
setting — so the 740213f0 inheritance pin in TestAdminCreateUser could never
pass and failed every full-suite run.

Also replace the TestAdminCreateUser "stable-ish" uniquifier (MaxConns is
pinned to 1 by the harness, so it produced the same user every run and
depended on the next run's cleanup sweep) with a real uuid suffix.

cmd/server/tests/ownership_and_admin_test.go

@@ -183,8 +183,10 @@ func (s *OwnershipAndAdminTestSuite) TestHighlightDelete_CrossUserNoOp() {
 // create accounts even with self-service registration disabled, regular
 // users cannot, and duplicates conflict.
 func (s *OwnershipAndAdminTestSuite) TestAdminCreateUser() {
-	suffix := fmt.Sprintf("%d", s.setup.DBPool.Config().MaxConns) // stable-ish uniquifier
-	unique := fmt.Sprintf("admincreated%s", suffix)
+	// Real unique suffix: MaxConns is forced to 1 by the harness, so the old
+	// "stable-ish" uniquifier produced the same user every run and only
+	// survived on the setup-time cleanup sweep of the NEXT run.
+	unique := fmt.Sprintf("admincreated-%s", uuid.New().String()[:8])
 
 	// Regular user token → 403 (AdminMiddleware).
 	payload, _ := json.Marshal(map[string]interface{}{