Name the reaper's hard delete in the event body comments (closes #455)

The comments on eventBodyQuery and on TestHandleEventBodyDownload_ReapedEvent404s credited the soft-delete predicate for refusing a reaped event. The retention reaper deletes event rows outright and nothing soft-deletes an event, so a reaped event is simply gone. Both comments now say so; the test's "soft deleted" case is described as pinning the query's deleted_at predicate for a row no code produces today. Comments only.

Model: opus-5-5

internal/handlers/event_body.go

@@ -15,10 +15,12 @@ import (
 // eventBodyQuery reads one event's stored body as bytes. The cast
 // to blob is what makes the driver hand back the stored bytes
 // rather than a string conversion, so Content-Length taken from
-// the result matches what goes on the wire. The soft-delete
-// predicate is spelled out because Raw bypasses GORM's default
-// scope, and it is what stops a reaped event still being
-// downloadable.
+// the result matches what goes on the wire. The retention reaper
+// deletes event rows outright, so a reaped event is simply gone
+// and the query finds no row. The deleted_at predicate repeats
+// the soft-delete scope GORM adds to its own queries, which Raw
+// bypasses; nothing soft-deletes an event, so today it excludes
+// nothing.
 const eventBodyQuery = "SELECT cast(body as blob) " +
 	"FROM events WHERE id = ? AND webhook_id = ? AND deleted_at IS NULL"