feat(webui): server-side SVG charts + reanimator-chart viewer

Metrics:
- Replace canvas JS charts with server-side SVG via go-analyze/charts
- Add ring buffers (120 samples) for CPU temp and power
- /api/metrics/chart/{name}.svg endpoint serves live SVG, polled every 2s

Dashboard:
- Replace custom renderViewerPage with viewer.RenderHTML() from reanimator/chart submodule
- Mount chart static assets at /chart/static/

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

audit/internal/webui/api.go

@@ -423,6 +423,16 @@ func (h *handler) handleAPIMetricsStream(w http.ResponseWriter, r *http.Request)
 			return
 		case <-ticker.C:
 			sample := platform.SampleLiveMetrics()
+
+			// Feed ring buffers for server-side SVG charts
+			for _, t := range sample.Temps {
+				if t.Name == "CPU" {
+					h.ringCPUTemp.push(t.Celsius)
+					break
+				}
+			}
+			h.ringPower.push(sample.PowerW)
+
 			b, err := json.Marshal(sample)
 			if err != nil {
 				continue