feat(identity): content unit data hygiene — specials, provisional promotion, duplicate merge (DH-1)

- metadata.includeSpecials (default true): full refresh and the language
  backfill fetch TMDB season 0 (specials) when present, like MP; season 0
  stays out of the episode-total ledger
- refreshMetadata promotes provisional season/episode units that match the
  TMDB season/episode layout to confirmed (source=tmdb), keeping ids and all
  references; non-matching units stay provisional
- content_unit.source (migration 0053): release / file / tmdb / user
- duplicate units (same entity/kind/season/episode/content type/segment) are
  merged as a refresh step and via `scripts/identity-cleanup.ts
  --merge-duplicates` (dry-run by default); keeper = most referenced, then
  confirmed, then earliest; references auto-discovered via FKs and repointed
- ensureUnits takes a per-unit advisory xact lock to stop concurrent lazy
  creation from producing duplicates
- runbooks updated; user DB read-only dry-run: 征途 S01E09/E10 4 units each
  -> 1 each (6 removed), not applied

Co-Authored-By: Claude Opus 5.5 <[email protected]>

apps/server/test/e2e/e7-tv-series.test.ts

@@ -296,8 +296,9 @@ describe.skipIf(!hasPg)("E7 常规剧集纵切", () => {
       .where("season_number", "=", 1)
       .orderBy("episode_number")
       .execute();
+    // DH-1:元数据刷新拉了 S1 季详情,对上 TMDB 的 E01 转正式;E02 不在 mock TMDB 的 S1 里,保持临时
     expect(eps).toEqual([
-      { episode_number: 1, status: "provisional" },
+      { episode_number: 1, status: "confirmed" },
       { episode_number: 2, status: "provisional" },
     ]);
     // 第三集没出现、总集数未知:Slot 不满足,订阅继续追踪