refactor(auth): remove actions re-export from server barrel to avoid next/headers import issue

- update barrel comment to document why actions.js is excluded
- remove re-exports of server actions that depend on `next/headers` at module load time
- instruct consumers to import actions explicitly via @zen/core/features/auth/actions

src/features/auth/index.js

@@ -1,6 +1,10 @@
 /**
- * Zen Authentication — server barrel.
- * Server actions live in @zen/core/features/auth/actions.
+ * Zen Authentication — server barrel (Next.js-free).
+ *
+ * Does NOT re-export actions.js — that file imports `next/headers` at the
+ * top level and cannot be pulled in via this barrel (which is imported by
+ * external modules during instrumentation, before Next.js aliases are active).
+ * Import server actions explicitly via @zen/core/features/auth/actions.
  */
 
 export {
@@ -39,16 +43,3 @@ export {
   generateToken,
   generateId
 } from './password.js';
-
-export {
-  registerAction,
-  loginAction,
-  logoutAction,
-  getSession,
-  forgotPasswordAction,
-  resetPasswordAction,
-  verifyEmailAction,
-  setupAccountAction,
-  setSessionCookie,
-  refreshSessionCookie
-} from './actions.js';