feat(metadata): overview falls back to Chinese variants only (MD-2)

- adapters: overviewLanguages() limits overview/tagline chain to Chinese
  variants (zh-CN→zh-SG→zh-TW→zh-HK); titles keep full chain; season
  supplement fetch skips languages useless for overview
- setting metadata.overviewNonChineseFallback (default off) + UI switch
- media detail shows "暂无简介" for empty entity/episode overview
- scripts/overview-recompute.ts: recompute stored non-Chinese overviews
  from kv_cache only (no TMDB requests), dry-run by default, --apply
- tests: chain unit tests, Heart Signal (103147) fixture, server
  recompute test, MP differential for episode overview
- runbook + CHANGELOG

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

apps/server/src/modules/acquisition-organize/ports.ts

@@ -23,7 +23,7 @@ import {
   createEntityFromTmdbCandidate,
   enqueueNewEntityRefresh,
 } from "../sources-identity/service/entity-from-candidate.ts";
-import { metadataLanguages } from "../sources-identity/service/metadata-rich.ts";
+import { metadataLanguages, metadataTextOptions } from "../sources-identity/service/metadata-rich.ts";
 import { identifyParsed, type NameIdentifyResult } from "../sources-identity/service/resolve.ts";
 import type { ServerContext } from "../types.ts";
 
@@ -133,7 +133,7 @@ export function createPorts(
         () => rt().tmdb(),
         { kind: ref.type, externalId: ref.id },
         { type, id: actor.id },
-        { languages: await metadataLanguages(ctx) },
+        { languages: await metadataLanguages(ctx), ...(await metadataTextOptions(ctx)) },
       );
       if (r.created) await enqueueNewEntityRefresh(ctx, r.mediaEntityId);
       return r.mediaEntityId;