fix(crawler): queue chapter content in ascending number order (0.51.1)

Both enqueue paths now order by chapters.number so the cron tick and the
bookmark hook insert jobs from chapter 1 upward instead of source-discovery
or random-UUID order. The lease query tiebreaks on created_at so jobs
sharing a batch's scheduled_at come off the queue in insertion order,
propagating the enqueue intent through to dequeue. Concurrent workers
and per-CDN latency can still drift actual completion order.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

backend/src/crawler/jobs.rs

@@ -104,6 +104,12 @@ pub async fn enqueue(pool: &PgPool, payload: &JobPayload) -> sqlx::Result<Enqueu
 ///
 /// `kind_filter` matches against `payload->>'kind'`; `None` means
 /// any kind.
+///
+/// Ties on `scheduled_at` (the common case: a cron batch enqueues
+/// everything with the same default `now()`) break by `created_at`, so
+/// jobs come off the queue in insertion order. The enqueue paths insert
+/// chapter-content jobs in ascending `chapters.number` order, so this
+/// tiebreaker is what propagates that intent through to dequeue.
 pub async fn lease(
     pool: &PgPool,
     kind_filter: Option<&str>,
@@ -118,7 +124,7 @@ pub async fn lease(
              WHERE (state = 'pending' OR (state = 'running' AND leased_until < now()))
                AND scheduled_at <= now()
                AND ($1::text IS NULL OR payload->>'kind' = $1)
-             ORDER BY scheduled_at
+             ORDER BY scheduled_at, created_at
              LIMIT $2
              FOR UPDATE SKIP LOCKED
         )