feat(dashboard): add real system metrics endpoint and fix UI dark-theme issues

- Add /api/system/metrics endpoint reading real data from /proc (CPU, memory, disk, network, load avg, uptime, connections)
- Replace hardcoded fake monitoring metrics with live API data
- Replace random chart data with real latency/error-rate/client-request charts from DB logs
- Fix light-mode colors leaking into dark theme (monitoring stream bg, settings tokens, warning card)
- Add 'models' to page title map, fix System Health card structure
- Move inline styles to CSS classes (monitoring-layout, monitoring-stream, token-item, warning-card)
- Prevent duplicate style injection in monitoring page

static/css/dashboard.css

@@ -1120,3 +1120,41 @@ body {
 ::-webkit-scrollbar-thumb:hover {
     background: var(--bg4);
 }
+
+/* Monitoring Layout */
+.monitoring-layout {
+    display: grid;
+    grid-template-columns: 2fr 1fr;
+    gap: 1.5rem;
+}
+
+.monitoring-stream {
+    height: 400px;
+    overflow-y: auto;
+    background-color: var(--bg-secondary);
+    border: 1px solid var(--border-color);
+    border-radius: var(--border-radius);
+    margin-top: 1rem;
+    padding: 1rem;
+}
+
+.monitoring-charts {
+    margin-top: 1.5rem;
+}
+
+/* Settings: Token Items */
+.token-item {
+    display: flex;
+    gap: 0.5rem;
+    align-items: center;
+    background: var(--bg0);
+    padding: 0.5rem;
+    border-radius: 6px;
+    border: 1px solid var(--bg2);
+}
+
+/* Settings: Warning Card */
+.warning-card {
+    border: 1px dashed var(--warning);
+    background: rgba(215, 153, 33, 0.08);
+}