feat(sites): 站点请求失败留样(site_failure_sample,每站最近 5 份)

- 迁移 0077 新表 site_failure_sample:类型(parse_error / challenge)、请求类型、脱敏 URL、状态码、
  关键响应头、错误文案、命中规则、脱敏页面开头(≤ 64 KB);样本几十 KB,不放进每条请求都读的 site.config
- 适配器 onFailureSample 回调接到 runtime.siteAdapter,异步写入并删到最近 5 份,写失败只记日志
- GET /sites/{id}/failure-samples(不带正文)与 /failure-samples/{sampleId}(带正文)

Co-Authored-By: Claude Opus 5.5 <[email protected]>
Claude-Session: https://claude.ai/code/session_01Cxwgnn2pbzQ7rXv3rq7fei

packages/contracts/test/db-sync.test.ts

@@ -105,6 +105,7 @@ const ROWS: Record<string, { row: Obj; dbOnly?: string[]; apiOnly?: string[] }>
   MetadataEnrichment: { row: C.MetadataEnrichment },
   ResolutionAttempt: { row: C.ResolutionAttempt },
   SiteSnapshot: { row: C.SiteSnapshot },
+  SiteFailureSample: { row: C.SiteFailureSample },
   // W4-C 浏览器实体(0023)
   // BR-4:identity 是浏览器固定身份的缓存(站点请求 UA 用),不进 API
   BrowserProvider: { row: C.BrowserProviderRow, dbOnly: ["identity"] },
@@ -252,6 +253,7 @@ const ENUMS: Record<string, z.ZodEnum> = {
   ScheduledJobLastStatus: C.ScheduleRunStatus,
   ScheduledJobRunTrigger: C.ScheduleTrigger,
   ScheduledJobRunStatus: C.ScheduleRunStatus,
+  SiteFailureSampleKind: C.SiteFailureSampleKind,
   ScrapeRecordStatus: C.ScrapeStatus,
   ScrapeRecordTrigger: C.ScrapeTrigger,
   SubtitleWriteSource: C.SubtitleSource,