Seed the retention tests 50 rows per insert, not 500 (closes #198)

internal/database was the slowest test package, and three retention tests were nearly all of it. Most of their time went to seeding thousands of rows 500 per INSERT: the SQLite driver finds each parameter's value by scanning all of the statement's arguments, so binding grows with the square of the parameter count, and a 500-row insert carries several thousand. Seeding 50 rows per insert stores the same rows. No test case or assertion changes. The header of script/test records the new figures; its 90s timeout stays.

Model: opus-5-5

internal/database/totals_test.go

@@ -102,6 +102,12 @@ func TestWebhookDBManager_TotalsSurviveReopen(t *testing.T) {
 // seedExpiredEvents stores count events created at the given time,
 // each with a delivered delivery to one target and a failed delivery
 // to the other, and one attempt for each delivery.
+//
+// It and seedBareEvents insert 50 rows per statement, not more. The
+// SQLite driver looks up each parameter's value by scanning all of the
+// statement's arguments, so the time to bind a statement grows with the
+// square of its parameter count: at 500 rows, several thousand
+// parameters, the seeding took most of these tests' time under -race.
 func seedExpiredEvents(
 	t *testing.T,
 	db *gorm.DB,
@@ -138,8 +144,8 @@ func seedExpiredEvents(
 		)
 	}
 
-	require.NoError(t, db.CreateInBatches(events, 500).Error)
-	require.NoError(t, db.CreateInBatches(deliveries, 500).Error)
+	require.NoError(t, db.CreateInBatches(events, 50).Error)
+	require.NoError(t, db.CreateInBatches(deliveries, 50).Error)
 
 	results := make([]database.DeliveryResult, len(deliveries))
 	for i := range deliveries {
@@ -148,7 +154,7 @@ func seedExpiredEvents(
 		}
 	}
 
-	require.NoError(t, db.CreateInBatches(results, 500).Error)
+	require.NoError(t, db.CreateInBatches(results, 50).Error)
 }
 
 // seedBareEvents stores count events created at the given time, with
@@ -172,7 +178,7 @@ func seedBareEvents(
 		events[i].CreatedAt = createdAt
 	}
 
-	require.NoError(t, db.CreateInBatches(events, 500).Error)
+	require.NoError(t, db.CreateInBatches(events, 50).Error)
 }
 
 // TestRetentionReaper_PrunesMoreThanOneBatch verifies that a prune