feat(crawler): reconcile pass to enqueue mangas missing from the DB (0.85.0)

The interleaved metadata pass misses mangas to list drift (a title slips a
pagination slot during the slow detail walk). Add a reconcile pass: a cheap,
full, list-only walk (refs only, no detail visit, no early stop) that
set-diffs the walked keys against manga_sources and enqueues the strictly-
missing ones as SyncManga jobs. A set-diff is immune to drift — a manga only
has to appear somewhere in the list.

- Build the previously-dead SyncManga worker by extending RealChapterDispatcher
  to run the shared pipeline::process_manga_ref (fetch → upsert → cover →
  chapters), refactored out of run_metadata_pass so both paths stay in lockstep.
  The crawl worker now leases both sync_chapter_content and sync_manga
  (jobs::lease_kinds); both serialize on the single exclusive browser.
- SyncManga payload carries url + title so the worker can rebuild the ref and
  the dead-jobs/history UI can label a missing manga that has no manga row yet.
- "Missing" = strict NOT EXISTS (dropped rows count as present). Re-enqueue is
  skipped when a pending/running/dead SyncManga job already exists, so a gone
  manga (detail 404 → retries → dead) is left dead and not retried.
- New POST /v1/admin/crawler/reconcile (fire-and-forget, shares
  manual_pass_lock) + "Reconcile missing" admin button + Reconciling status
  phase streamed over SSE.
- dead-jobs/history queries surface payload title/url/key; tables fall back to
  them for sync_manga rows; both searches match the payload title.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

backend/src/crawler/status.rs

@@ -41,6 +41,10 @@ pub enum Phase {
     /// Backfilling covers that failed on first attempt. `index`/`total`
     /// track progress through this tick's batch.
     CoverBackfill { index: usize, total: usize },
+    /// Reconcile pass: walking the full source list (refs only, no detail
+    /// visit) to find mangas missing from the DB. `walked` is refs seen so
+    /// far this walk; `enqueued` is missing mangas queued as `SyncManga`.
+    Reconciling { walked: usize, enqueued: usize },
 }
 
 /// A chapter being downloaded right now, with a live page count. Keyed in