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/Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name = "mangalord"
-version = "0.51.0"
+version = "0.51.1"
 edition = "2021"
 default-run = "mangalord"