feat(identity): source-aware short-drama enrichment with snippet mode and hit rate (META-2)

- classify enrich sources: encyclopedia, platform pages (hongguo, kuaikaw, video
  platforms), douban (search snippet only) and other sites' search snippets
  (snippet mode, pages never opened); one extractor per source, fields carry
  source kind and confidence, merged by noisy-OR across hosts
- new cast field (applied as MediaCredit with placeholder ids)
- robots.txt check (cached per host 1 day) and login-wall/captcha give-up
- per-enrichment source attempts + GET /identity/enrich-stats, 30-day hit-rate
  table under settings -> metadata -> identity
- setting identity.enrichSnippetAllSites (default on); default domains add
  baike.com and kuaikaw.cn
- replay fixtures from the real run on the 4 user-library short dramas
  (sanitized Brave responses, hongguo page, robots.txt)

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

packages/contracts/src/capability.ts

@@ -581,7 +581,7 @@ export const CAPABILITY_CATALOG: Record<KnownCapabilityId, CapabilityDescriptor>
   "metadata.enrich": d(
     "metadata.enrich",
     "补全元数据",
-    "TMDB 查不到的作品（短剧、平台独播剧）按标题查网页：搜索后只读白名单网站（平台、百科），抽取标题、别名、年份、平台、集数、简介、海报、类型，每个字段带出处和证据等级。只给建议，不改作品；同一标题 7 天内直接返回上次结果",
+    "TMDB 查不到的作品（短剧、平台独播剧）按标题查网页：搜索后读白名单网站（平台、百科，遵守 robots.txt），豆瓣和其它网站只用搜索摘要，抽取标题、别名、年份、平台、集数、主演、简介、海报、类型，每个字段带出处、置信度和证据等级。只给建议，不改作品；同一标题 7 天内直接返回上次结果",
     "propose",
     "MetadataEnrich",
     "organize.execute",