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]>

packages/contracts/src/settings.ts

@@ -226,6 +226,11 @@ export const MetadataSettings = z.object({
     .min(1)
     .max(8)
     .default(["zh-CN", "zh-SG", "zh-TW", "zh-HK", "en-US"]),
+  /**
+   * DH-1 季 0(特别篇):true = full 刷新与元数据回刷在 TMDB 有季 0 时一并拉取每集信息并建集单元(对照 MP);
+   * 季 0 不计入正片季总集数与订阅完成判定
+   */
+  includeSpecials: z.boolean().default(true),
 });
 export type MetadataSettings = z.infer<typeof MetadataSettings>;
 
@@ -611,7 +616,12 @@ export const DEFAULT_SETTINGS: GlobalSettings = {
     sessionDir: null,
     webSearch: DEFAULT_WEB_SEARCH,
   },
-  metadata: { tmdbApiKeySecretRef: null, tmdbBaseUrl: null, languages: ["zh-CN", "zh-SG", "zh-TW", "zh-HK", "en-US"] },
+  metadata: {
+    tmdbApiKeySecretRef: null,
+    tmdbBaseUrl: null,
+    languages: ["zh-CN", "zh-SG", "zh-TW", "zh-HK", "en-US"],
+    includeSpecials: true,
+  },
   sites: {
     defaultRateLimit: { requestsPerMinute: 20, concurrency: 2 },
     defaultSnapshotIntervalSec: 3600,
@@ -906,6 +916,7 @@ export const SETTINGS_SECTIONS: readonly SettingsSectionDef[] = [
       "metadata.tmdbApiKeySecretRef",
       "metadata.tmdbBaseUrl",
       "metadata.languages",
+      "metadata.includeSpecials",
       "cache.tmdbMaxSize",
       "identity.eagerTmdbLookup",
       "identity.autoEnrich",