fix(crawler): scope dispatch_target to live sources, newest first (0.36.4)

The chapter dispatcher's URL resolver had no dropped_at filter and no
ORDER BY — a chapter whose only chapter_sources row had been soft-
dropped was still dispatched against the stale URL, eating retry
budget on guaranteed transients. With multiple live sources the LIMIT
1 winner was nondeterministic.

Add `AND cs.dropped_at IS NULL` and `ORDER BY cs.last_seen_at DESC`
to dispatch_target, bringing it in lockstep with the enqueue queries
in pipeline.rs that already filter on dropped_at. Returns None when
all sources are dropped — callers in daemon.rs already treat None
as "ack the job, skip the work."

Tests in tests/repo_chapter.rs cover the three branches (freshest
live wins, dropped sources skipped, all-dropped returns None).

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

frontend/package.json

@@ -1,6 +1,6 @@
 {
   "name": "mangalord-frontend",
-  "version": "0.36.3",
+  "version": "0.36.4",
   "private": true,
   "type": "module",
   "scripts": {