fix: align AgentHealth page with mock design

- DetailPanel: switch from tabs to flat children layout (fixes stale
  tab state bug), add position:fixed override, key on agent id
- Stat strip: colored status breakdown (live/stale/dead), msg/s detail
  on TPS, "requires attention" on dead count
- Scope trail: simplified to "X/Y live" label
- Event card header: rename "Event Log" to "Timeline" with count badge
- Remove unused Breadcrumb, scopeItems, groupHealth

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

ui/src/pages/AgentHealth/AgentHealth.module.css

@@ -244,3 +244,36 @@
   font-size: 12px;
   color: var(--text-muted);
 }
+
+/* Status breakdown in stat card */
+.statusBreakdown {
+  display: flex;
+  gap: 8px;
+  font-size: 11px;
+}
+
+.statusLive { color: var(--success); }
+.statusStale { color: var(--warning); }
+.statusDead { color: var(--error); }
+
+/* Scope trail */
+.scopeLabel {
+  font-size: 13px;
+  font-weight: 600;
+  color: var(--text-secondary);
+}
+
+/* DetailPanel override */
+.detailPanelOverride {
+  position: fixed;
+  top: 0;
+  right: 0;
+  height: 100vh;
+  z-index: 100;
+  box-shadow: -4px 0 24px rgba(0, 0, 0, 0.12);
+}
+
+.panelDivider {
+  border-top: 1px solid var(--border-subtle);
+  margin: 16px 0;
+}