feat: add task history diagnostics

src/components/frontend/public/style.css

@@ -671,6 +671,7 @@ h2 { font-size: 14px; text-transform: uppercase; letter-spacing: 0.08em; }
 
 .table-wrap { overflow: auto; max-height: calc(100vh - 174px); }
 table { width: 100%; border-collapse: collapse; min-width: 760px; }
+.task-history-table { min-width: 1080px; }
 th, td {
   padding: 7px 9px;
   border-bottom: 1px solid var(--line-soft);
@@ -689,6 +690,44 @@ th {
 }
 td { color: var(--text); }
 
+.task-duration {
+  display: grid;
+  gap: 2px;
+  min-width: 118px;
+}
+.task-duration strong {
+  color: var(--accent-2);
+  font-family: "Cascadia Mono", "IBM Plex Mono", "Liberation Mono", monospace;
+  font-size: 13px;
+}
+.task-duration span {
+  color: var(--muted);
+  font-size: 11px;
+}
+.task-diagnostic {
+  display: grid;
+  gap: 4px;
+  min-width: 190px;
+  max-width: 360px;
+}
+.task-diagnostic b {
+  font-size: 11px;
+  letter-spacing: 0.1em;
+  text-transform: uppercase;
+}
+.task-diagnostic.ok b { color: var(--ok); }
+.task-diagnostic.warn b { color: var(--warn); }
+.task-diagnostic.failed b { color: var(--danger); }
+.diagnostic-reason {
+  color: #ffd7cf;
+  overflow-wrap: anywhere;
+}
+.diagnostic-meta {
+  display: flex;
+  flex-wrap: wrap;
+  gap: 4px;
+}
+
 .compact-row, .heartbeat-row, .log-row, .endpoint-list article, .policy-grid article {
   display: grid;
   grid-template-columns: auto minmax(180px, 1fr) auto auto;