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/api.ts

@@ -2200,6 +2200,15 @@ export const Api = {
       body: identity.EnrichApplyInput,
       response: identity.EnrichApplyResult,
     }),
+    // META-2 补全命中率(按来源类别)
+    enrichStats: ep({
+      method: "get",
+      path: "/identity/enrich-stats",
+      scope: "read",
+      summary: "元数据补全命中率（最近 N 天，按来源类别：百科、平台、豆瓣摘要、其它网站摘要）",
+      query: identity.EnrichStatsQuery,
+      response: identity.EnrichStats,
+    }),
   },
 
   // ── 媒体库 / 库存 / 首页 ──