fix(crawler): quarantine recently-dead chapters from re-enqueue (0.35.4)

The partial dedup index only blocks (pending|running) duplicates, so
once a SyncChapterContent job transitions to 'dead' (max_attempts
exhausted) the slot frees. Every subsequent cron tick re-enqueued the
chapter — page_count = 0 and dropped_at IS NULL stay true — burned
another max_attempts retries, and died again. Permanent-failure
chapters spun forever.

enqueue_bookmarked_pending and enqueue_pending_for_manga now skip
chapters whose latest sync_chapter_content job is dead within
CHAPTER_DEAD_QUARANTINE_DAYS (7). A failed chapter goes silent for a
week, then gets one more shot — long enough for a transient site
issue to resolve, short enough that permanent failures don't stay
permanent if conditions change.

Two integration tests pin both halves of the contract.

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

frontend/package.json

@@ -1,6 +1,6 @@
 {
   "name": "mangalord-frontend",
-  "version": "0.35.3",
+  "version": "0.35.4",
   "private": true,
   "type": "module",
   "scripts": {