refactor(storage): replace configureStorageApi with additive registration pattern

src/features/auth/storage-policies.js

@@ -0,0 +1,11 @@
+/**
+ * Auth feature — storage access policies.
+ *
+ * Registered during initializeZen() via registerStoragePolicies().
+ * The auth feature owns its access rules; core/storage stays generic.
+ */
+
+export const storageAccessPolicies = [
+  // users/{userId}/... — seul le propriétaire ou un admin peut accéder
+  { prefix: 'users', type: 'owner' },
+];