Record response status per path; mark 404 trails red in the viewer

Document GETs now stash their status (200/404) in a pending table,
consumed by the matching ping: visits gain a per-path statuses map and
crawler hits a status field. Trail links with a 404 status render in
red with the status code in the tooltip, alongside the read time.

frontend/src/AnalyticsView.vue

@@ -425,6 +425,11 @@ const abuseRows = computed(() => formatAbuseRows(rangeData.value?.abuse || [], c
   margin-left: 0.5rem;
 }
 
+.analytics-view :deep(.trail-link.error),
+.analytics-view :deep(.trail-link.error:hover) {
+  color: var(--error, #c00);
+}
+
 .visit-table .utm-tag {
   display: inline-block;
   max-width: 100%;