Clear dead feeds from the Directory once a day, not before every scan (#193)

stale_unsubscribed takes the newest item of every unsubscribed feed, 2-5 s
warm and up to 12 s in production, and reap ran it before each scan, every
few minutes, holding up the sequential worker's scans and downloads. Its
thresholds are a month dead and a year quiet, so a day is plenty. Kept in
memory: a restart looks again at once.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

CHANGELOG.md

@@ -22,6 +22,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ### Fixed
 
+- Checking for new episodes no longer waits up to 12 seconds each time on a clear-out of dead feeds from the Directory, which now runs once a day (#193).
 - All Subscriptions, and every item list, comes up faster, most of all the first time after a quiet spell: it took half a second to two (#188).
 
 ### Security