fix(crawler): reap dead jobs alongside done ones

The retention reaper deleted only `state = 'done'` rows, so terminal
`dead` jobs (retries exhausted) accumulated in crawler_jobs forever —
slow unbounded table growth. Both states are end-of-life and never
leased again.

Rename `reap_done` → `reap_terminal` and broaden the filter to
`state IN ('done','dead')`; `pending`/`running` stay untouched. Test
extended to assert old done + old dead both reap while fresh terminal and
old-but-active rows survive.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

backend/src/crawler/daemon.rs

@@ -301,9 +301,9 @@ impl CronContext {
                 }
                 Err(e) => tracing::error!(?e, "cron: enqueue_bookmarked_pending failed"),
             }
-            match jobs::reap_done(pool, retention_days).await {
-                Ok(n) => tracing::info!(reaped = n, "cron: done-job reaper finished"),
-                Err(e) => tracing::error!(?e, "cron: done-job reaper failed"),
+            match jobs::reap_terminal(pool, retention_days).await {
+                Ok(n) => tracing::info!(reaped = n, "cron: terminal-job reaper finished"),
+                Err(e) => tracing::error!(?e, "cron: terminal-job reaper failed"),
             }
             match crate::repo::crawl_metrics::reap(pool, metrics_retention_days).await {
                 Ok(n) => tracing::info!(reaped = n, "cron: crawl-metrics reaper finished"),