fix: make preview env optional

env/schema.mjs

@@ -10,8 +10,8 @@ export const serverSchema = z.object({
   CMS_API_KEY: z.string(),
   CMS_ENVIRONMENT: z.enum(["development", "production", "staging", "test"]),
   CMS_URL: z.string(),
-  CMS_PREVIEW_URL: z.string(),
-  CMS_PREVIEW_TOKEN: z.string(),
+  CMS_PREVIEW_URL: z.string().optional(),
+  CMS_PREVIEW_TOKEN: z.string().optional(),
   NODE_ENV: z.enum(["development", "test", "production"]),
   PRINT_QUERY: z.boolean().default(false),
 });