style: add CSS modules to all pages matching design system mock layouts

Replace inline styles with semantic CSS module classes for proper visual
structure: card wrappers with borders/shadows, grid layouts for stat
strips and charts, section headers, and typography classes.

Pages updated: Dashboard, ExchangeDetail, RoutesMetrics, AgentHealth,
AgentInstance.

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

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

@@ -0,0 +1,66 @@
+.statStrip {
+  display: grid;
+  grid-template-columns: repeat(4, 1fr);
+  gap: 10px;
+  margin-bottom: 16px;
+}
+
+.groupGrid {
+  display: grid;
+  grid-template-columns: 1fr 1fr;
+  gap: 14px;
+  margin-bottom: 20px;
+}
+
+.instanceRow {
+  display: flex;
+  align-items: center;
+  gap: 8px;
+  padding: 8px 12px;
+  cursor: pointer;
+  transition: background 0.1s;
+  border-bottom: 1px solid var(--border-subtle);
+  font-size: 12px;
+}
+
+.instanceRow:last-child {
+  border-bottom: none;
+}
+
+.instanceRow:hover {
+  background: var(--bg-hover);
+}
+
+.instanceName {
+  font-weight: 600;
+  color: var(--text-primary);
+}
+
+.instanceTps {
+  margin-left: auto;
+  font-size: 11px;
+  font-family: var(--font-mono);
+  color: var(--text-muted);
+}
+
+.eventCard {
+  background: var(--bg-surface);
+  border: 1px solid var(--border-subtle);
+  border-radius: var(--radius-lg);
+  box-shadow: var(--shadow-card);
+  overflow: hidden;
+  display: flex;
+  flex-direction: column;
+  max-height: 420px;
+}
+
+.eventCardHeader {
+  display: flex;
+  align-items: center;
+  justify-content: space-between;
+  padding: 10px 16px;
+  border-bottom: 1px solid var(--border-subtle);
+  font-size: 13px;
+  font-weight: 600;
+  color: var(--text-primary);
+}