chore(poll): restore 6h upstream poll cadence

The hourly cadence was a temporary measure for fast feedback while
debugging the build failures. Builds are green and publishing, so revert
to the standard 6h trigger.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

.gitea/workflows/poll-upstream.yml

@@ -2,7 +2,7 @@ name: poll-upstream
 
 on:
   schedule:
-    - cron: "0 * * * *"
+    - cron: "0 */6 * * *"
   workflow_dispatch: {}
 
 concurrency: