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/web/app/components/settings/metadata.tsx

@@ -54,16 +54,25 @@ const TMDB_CARD: CardSpec = {
       hint: "标题、简介和每集信息按顺序取第一个有值的语言；中文名取链中第一个中文值。逗号分隔，如 zh-CN, zh-SG",
       wide: true,
     },
+    {
+      name: "metadata.includeSpecials",
+      label: "包含特别篇（季 0）",
+      kind: "switch",
+      hint: "全量刷新和元数据回刷时，TMDB 有季 0 就一并拉取每集信息。特别篇不计入正片季的总集数和订阅完成判定",
+      wide: true,
+    },
   ],
   fromSettings: (s) => ({
     "metadata.tmdbApiKey": "",
     "metadata.tmdbBaseUrl": s.metadata.tmdbBaseUrl ?? "",
     "metadata.languages": (s.metadata.languages ?? DEFAULT_LANGUAGES).join(", "),
+    "metadata.includeSpecials": s.metadata.includeSpecials !== false,
   }),
   toPatch: (v) => ({
     metadata: {
       tmdbBaseUrl: str(v["metadata.tmdbBaseUrl"]) || null,
       languages: parseLanguages(str(v["metadata.languages"])),
+      includeSpecials: v["metadata.includeSpecials"] === true,
       ...(str(v["metadata.tmdbApiKey"]) ? { tmdbApiKey: str(v["metadata.tmdbApiKey"]) } : {}),
     },
   }),