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/analysis_worker.rs

@@ -158,6 +158,16 @@ async fn worker_reanalyzes_done_page_when_forced(pool: PgPool) {
     handle.shutdown().await;
 
     assert_eq!(dispatcher.call_count(), 1, "force must re-dispatch");
+
+    // The worker stamps how long the dispatch took onto the existing row
+    // (recorded after ack; shutdown has awaited the in-flight job).
+    let dur: Option<i64> =
+        sqlx::query_scalar("SELECT duration_ms FROM page_analysis WHERE page_id = $1")
+            .bind(page_id)
+            .fetch_one(&pool)
+            .await
+            .unwrap();
+    assert!(dur.is_some(), "worker should record analysis duration_ms");
 }
 
 #[sqlx::test(migrations = "./migrations")]