chore: standardize ESM-first architecture and resolve all type/test/lint errors

lib/env.ts

@@ -1,5 +1,5 @@
 import { z } from 'zod';
-import { validateMintelEnv, mintelEnvSchema } from '@mintel/next-utils';
+import { validateMintelEnv, mintelEnvSchema, withMintelRefinements } from '@mintel/next-utils';
 
 /**
  * Environment variable schema.
@@ -25,9 +25,9 @@ const envExtension = {
 };
 
 /**
- * Full schema including Mintel base
+ * Full schema including Mintel base and refinements
  */
-export const envSchema = z.object(mintelEnvSchema).extend(envExtension);
+export const envSchema = withMintelRefinements(z.object(mintelEnvSchema).extend(envExtension));
 
 /**
  * Validated environment object.