fix(ci): reduce poll frequency to hourly and stop cancelling prerelease builds

The 15-minute poll interval was re-dispatching builds before they could
finish. The prerelease workflow had cancel-in-progress: true which
cancelled the running build each time. Change poll to hourly and set
cancel-in-progress: false on prerelease builds so they run to completion.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

.gitea/workflows/poll-upstream.yml

@@ -2,7 +2,7 @@ name: poll-upstream
 
 on:
   schedule:
-    - cron: "*/15 * * * *"
+    - cron: "0 * * * *"
   workflow_dispatch: {}
 
 concurrency: