feat(admin): observability — job history, live "now analyzing", durations & metrics

Crawler + analysis admin dashboards gain a Live / History / Metrics
segmented view.

History: searchable, filterable, paginated job log per subsystem
(crawler_jobs across all states/kinds; page_analysis terminal outcomes),
with inline dead-job requeue and a Duration column.

Live: enrich analysis SSE events with manga title + chapter number and add
a sticky "Now analyzing" banner that jumps to and highlights the page.

Metrics: new durable crawl_metrics table (migration 0028) timing every
crawl op (manga list walk, manga detail, cover, whole chapter; per-page
derived from chapter) plus page_analysis.duration_ms for analysis. New
endpoints serve per-type average durations + success rates and a recent-ops
log; a cron reaper (CRAWL_METRICS_RETENTION_DAYS) bounds growth.

Tested: repo + API integration tests, vitest for the API client and
fmtDuration, and Playwright for the History/Metrics tabs.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

backend/tests/crawler_daemon.rs

@@ -39,6 +39,7 @@ fn make_cfg(
         daily_at: far_future_daily_at(),
         tz: Tz::UTC,
         retention_days: 7,
+        metrics_retention_days: 90,
         session_expired,
         status: mangalord::crawler::status::StatusHandle::new(workers),
         job_timeout: Duration::from_secs(60),