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]>

apps/server/test/fixtures/enrich/robots-hongguo.txt

@@ -0,0 +1,29 @@
+# hongguoduanju.com/robots.txt(2026-09-30 录制)
+User-agent: Googlebot
+Allow: /
+
+Disallow: /category?*background=
+Disallow: /category?*setting=
+Disallow: /category?*topic=
+Disallow: /category?*sort_type=
+Disallow: /category?*time=
+Disallow: /category?*gender=
+Disallow: /player/*/*
+Disallow: /series/
+Disallow: /query/
+
+User-agent: *
+Allow: /
+
+Disallow: /category?*background=
+Disallow: /category?*setting=
+Disallow: /category?*topic=
+Disallow: /category?*sort_type=
+Disallow: /category?*time=
+Disallow: /category?*gender=
+Disallow: /player/*/*
+Disallow: /series/
+
+Sitemap: https://hongguoduanju.com/seo-important.xml
+Sitemap: https://hongguoduanju.com/seo-static.xml
+Sitemap: https://hongguoduanju.com/sitemap/hongguoduanju/index.xml