Update registry.json

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

Author: bthos

registry.json

@@ -11,7 +11,7 @@
       "repository": "https://github.com/tmtrckr/plugin-billing",
       "latest_version": "1.0.0",
       "description": "Billable time tracking plugin for Time Tracker application.",
-      "category": "other",
+      "category": "billing",
       "verified": false,
       "downloads": 0,
       "tags": [],