feat(metrics): SQLite persistence + chart fixes (no dots, peak label, min/avg/max in title)

- Add modernc.org/sqlite dependency; write every sample to
  /appdata/bee/metrics.db (WAL mode, prune to 24h on startup)
- Pre-fill ring buffers from last 120 DB rows on startup so charts
  survive service restarts
- Ticker changed 3s→1s; chart JS refresh will be set to 2s (lag ≤3s)
- Add GET /api/metrics/export.csv for full history download
- Chart rendering: SymbolNone (no dots), right padding=80px so peak
  mark line label is not clipped, min/avg/max appended to chart title

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

audit/internal/webui/api.go

@@ -592,7 +592,7 @@ func (h *handler) handleAPIMetricsStream(w http.ResponseWriter, r *http.Request)
 	if !sseStart(w) {
 		return
 	}
-	ticker := time.NewTicker(3 * time.Second)
+	ticker := time.NewTicker(1 * time.Second)
 	defer ticker.Stop()
 	for {
 		select {
@@ -600,47 +600,10 @@ func (h *handler) handleAPIMetricsStream(w http.ResponseWriter, r *http.Request)
 			return
 		case <-ticker.C:
 			sample := platform.SampleLiveMetrics()
-
-			// Feed server ring buffers
-			for _, t := range sample.Temps {
-				switch t.Group {
-				case "cpu":
-					h.pushNamedMetricRing(&h.cpuTempRings, t.Name, t.Celsius)
-				case "ambient":
-					h.pushNamedMetricRing(&h.ambientTempRings, t.Name, t.Celsius)
-				}
+			h.feedRings(sample)
+			if h.metricsDB != nil {
+				_ = h.metricsDB.Write(sample)
 			}
-			h.ringPower.push(sample.PowerW)
-			h.ringCPULoad.push(sample.CPULoadPct)
-			h.ringMemLoad.push(sample.MemLoadPct)
-
-			// Feed fan ring buffers (grow on first sight)
-			h.ringsMu.Lock()
-			for i, fan := range sample.Fans {
-				for len(h.ringFans) <= i {
-					h.ringFans = append(h.ringFans, newMetricsRing(120))
-					h.fanNames = append(h.fanNames, fan.Name)
-				}
-				h.ringFans[i].push(float64(fan.RPM))
-			}
-			// Feed per-GPU ring buffers (grow on first sight)
-			for _, gpu := range sample.GPUs {
-				idx := gpu.GPUIndex
-				for len(h.gpuRings) <= idx {
-					h.gpuRings = append(h.gpuRings, &gpuRings{
-						Temp:    newMetricsRing(120),
-						Util:    newMetricsRing(120),
-						MemUtil: newMetricsRing(120),
-						Power:   newMetricsRing(120),
-					})
-				}
-				h.gpuRings[idx].Temp.push(gpu.TempC)
-				h.gpuRings[idx].Util.push(gpu.UsagePct)
-				h.gpuRings[idx].MemUtil.push(gpu.MemUsagePct)
-				h.gpuRings[idx].Power.push(gpu.PowerW)
-			}
-			h.ringsMu.Unlock()
-
 			b, err := json.Marshal(sample)
 			if err != nil {
 				continue
@@ -652,6 +615,46 @@ func (h *handler) handleAPIMetricsStream(w http.ResponseWriter, r *http.Request)
 	}
 }
 
+// feedRings pushes one sample into all in-memory ring buffers.
+func (h *handler) feedRings(sample platform.LiveMetricSample) {
+	for _, t := range sample.Temps {
+		switch t.Group {
+		case "cpu":
+			h.pushNamedMetricRing(&h.cpuTempRings, t.Name, t.Celsius)
+		case "ambient":
+			h.pushNamedMetricRing(&h.ambientTempRings, t.Name, t.Celsius)
+		}
+	}
+	h.ringPower.push(sample.PowerW)
+	h.ringCPULoad.push(sample.CPULoadPct)
+	h.ringMemLoad.push(sample.MemLoadPct)
+
+	h.ringsMu.Lock()
+	for i, fan := range sample.Fans {
+		for len(h.ringFans) <= i {
+			h.ringFans = append(h.ringFans, newMetricsRing(120))
+			h.fanNames = append(h.fanNames, fan.Name)
+		}
+		h.ringFans[i].push(float64(fan.RPM))
+	}
+	for _, gpu := range sample.GPUs {
+		idx := gpu.GPUIndex
+		for len(h.gpuRings) <= idx {
+			h.gpuRings = append(h.gpuRings, &gpuRings{
+				Temp:    newMetricsRing(120),
+				Util:    newMetricsRing(120),
+				MemUtil: newMetricsRing(120),
+				Power:   newMetricsRing(120),
+			})
+		}
+		h.gpuRings[idx].Temp.push(gpu.TempC)
+		h.gpuRings[idx].Util.push(gpu.UsagePct)
+		h.gpuRings[idx].MemUtil.push(gpu.MemUsagePct)
+		h.gpuRings[idx].Power.push(gpu.PowerW)
+	}
+	h.ringsMu.Unlock()
+}
+
 func (h *handler) pushNamedMetricRing(dst *[]*namedMetricsRing, name string, value float64) {
 	if name == "" {
 		return