docs: fix blog post format for v3.4.0

Author: hyochan

docs/blog/2025-12-29-3.4.0-purchasestate-cleanup.md

@@ -1,11 +1,12 @@
 ---
-slug: v3.4.0-purchasestate-cleanup
-title: v3.4.0 - PurchaseState Cleanup & API Consolidation
+slug: 3.4.0-purchasestate-cleanup
+title: 3.4.0 - PurchaseState Cleanup & API Consolidation
 authors: [hyochan]
 tags: [release, openiap, android, billing, breaking-change]
+date: 2025-12-29
 ---
 
-## v3.4.0 Release Notes
+# 3.4.0 Release Notes
 
 This release reflects [OpenIAP v1.3.11 updates](https://www.openiap.dev/docs/updates/notes#gql-1-3-11-google-1-3-21-apple-1-3-9), simplifying the `PurchaseState` enum and consolidating the Android billing API.