fix: align AgentInstance page with mock design

- Chart headers: add current value meta text (CPU %, memory MB, TPS,
  error rate, thread count) matching mock layout
- Bottom section: 2-column grid with log placeholder (left) and
  timeline events (right) matching mock layout
- Timeline header: show "Timeline" + event count like mock
- Remove duplicate EmptyState placeholder

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

ui/src/pages/AgentInstance/AgentInstance.module.css

@@ -145,3 +145,31 @@
   color: var(--text-primary);
   margin-bottom: 12px;
 }
+
+.chartMeta {
+  font-size: 11px;
+  font-weight: 500;
+  color: var(--text-muted);
+  font-family: var(--font-mono);
+}
+
+.bottomSection {
+  display: grid;
+  grid-template-columns: 1fr 1fr;
+  gap: 14px;
+  margin-bottom: 20px;
+}
+
+.eventCount {
+  font-size: 11px;
+  font-weight: 500;
+  color: var(--text-muted);
+  font-family: var(--font-mono);
+}
+
+.emptyEvents {
+  padding: 20px;
+  text-align: center;
+  font-size: 12px;
+  color: var(--text-muted);
+}