Append real-time stats to CPU/RAM charts on each 15s tick

Zero extra Prometheus queries - reuses existing instant stats data
to grow chart series between 60s range query refreshes.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

src/lib/useEventStream.ts

@@ -68,7 +68,28 @@ export function useEventStream() {
     es.addEventListener('stats', (e) => {
       try {
         const stats = JSON.parse(e.data);
-        setState(prev => ({ ...prev, stats }));
+        setState(prev => {
+          // Append latest stats as new chart data points (real-time feed)
+          if (prev.metrics) {
+            const now = Math.floor(Date.now() / 1000);
+            const sixHoursAgo = now - 6 * 3600;
+            const append = (series: Array<[number, number]>, value: number): Array<[number, number]> => {
+              const filtered = series.filter(([ts]) => ts > sixHoursAgo);
+              filtered.push([now, value]);
+              return filtered;
+            };
+            return {
+              ...prev,
+              stats,
+              metrics: {
+                ...prev.metrics,
+                cpu: append(prev.metrics.cpu, stats.cpu_percent),
+                ram: append(prev.metrics.ram, stats.ram_percent),
+              },
+            };
+          }
+          return { ...prev, stats };
+        });
       } catch { /* ignore */ }
     });