docs(spec): use canonical roles[] form in app visibility-predicate example

ADR-0068 D4 follow-up. The embedded `describe()` example shipped the
non-canonical, non-catalog pattern `os.user.role == "admin"`; users
copy-paste these. Switch to `'org_admin' in current_user.roles` so the
shipped example matches the canonical contract and passes role-catalog
validation.

Author: zhuangjianguo

packages/spec/src/ui/app.zod.ts

@@ -46,7 +46,7 @@ const BaseNavItemSchema = z.object({
    * Formula expression returning boolean. 
    * e.g. "user.is_admin || user.department == 'sales'"
    */
-  visible: ExpressionInputSchema.optional().describe('Visibility predicate (CEL). e.g. P`os.user.role == "admin"`'),
+  visible: ExpressionInputSchema.optional().describe('Visibility predicate (CEL). e.g. P`\'org_admin\' in current_user.roles`'),
 
   /** Permissions required to see/access this navigation item */
   requiredPermissions: z.array(z.string()).optional().describe('Permissions required to access this item'),