perf(ebooks): feed configured backfill workers

internal/ebooks/enrichment_queue.go

@@ -17,7 +17,7 @@ const (
 	maxEnrichmentRetry     = 24 * time.Hour
 	transientRetryBase     = 5 * time.Minute
 	skippedRetryHorizon    = 15 * time.Minute
-	claimCandidateWindow   = 64
+	claimCandidateWindow   = maxEnrichWorkers
 )
 
 type EnrichmentOutcome string

internal/ebooks/enrichment_queue_test.go

@@ -87,8 +87,8 @@ func TestEnrichmentQueueClaimQueryUsesAtomicLeasedClaims(t *testing.T) {
 			}
 		})
 	}
-	if claimCandidateWindow <= 0 || claimCandidateWindow > 256 {
-		t.Fatalf("claim candidate window = %d, want a fixed sane bound", claimCandidateWindow)
+	if claimCandidateWindow != maxEnrichWorkers {
+		t.Fatalf("claim candidate window = %d, want worker ceiling %d", claimCandidateWindow, maxEnrichWorkers)
 	}
 }