Fix front matter key so the PWA tag shows on the relaunch post

Docusaurus reads tags from 'tags', so 'tag: [pwa]' was silently ignored.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Qq2F8PG8miEBBpLCjUqXW2

Author: claude

blog/2026-03-30-relaunch-app-as-pwa/index.md

@@ -1,7 +1,7 @@
 ---
 title: "Relaunch App 'bonreader' as PWA 'BelegScan.at'"
 date: "2026-03-30"
-tag: [pwa]
+tags: [pwa]
 ---
 
 Our application has undergone a relaunch, and we are excited to introduce the new features as a Progressive Web App (PWA). This approach ensures a smoother user experience and greater accessibility.