fix(tenants-create): define $canUpdateTenant before form partial

The shared _form.phtml partial reads $canUpdateTenant for the per-theme
logo upload blocks added in 6e3fc63c, but create(default).phtml never
defined it — every visit to admin/tenants/create raised an undefined-
variable warning and a 500.

In create-mode the actor has full edit authority over the form they are
filling in (the create-authorize gate has already passed), so set
$canUpdateTenant = true before requiring _form.phtml. Mirrors the value
that edit($id).php derives from the EDIT_CONTEXT capabilities map.

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

pages/admin/tenants/create(default).phtml

@@ -46,6 +46,10 @@
     $customFieldTenantUuid = '';
     $customFieldDefinitions = [];
     $ignoreTabStorage = true;
+    // In create-mode the actor has full edit authority over the form they
+    // are filling in; the shared _form.phtml partial reads $canUpdateTenant
+    // for the logo/favicon upload blocks introduced in commit 6e3fc63c.
+    $canUpdateTenant = true;
     require __DIR__ . '/_form.phtml';
     ?>
   </section>