Fix metrics correctness, redesign stats page

- Replace stale snapshot read (GetCurrentMetrics) with live query
  (GetLiveMetrics) against sandboxes table — always returns correct
  zeros when no capsules are running
- Fix CPU reserved formula: running + starting only; paused VMs no
  longer contribute vCPUs (RAM reservation for paused unchanged)
- Merge top cards into 3 paired Now/Peak cards with colored accent
  borders (green/blue/amber matching chart colors)
- Move Live badge from Running Capsules card to page-level header
- Add colored category dots to card and chart headers
- Charts stacked vertically, flex-1 to fill remaining page height
- vCPUs chart color changed to blue (#5a9fd4), RAM stays amber

internal/api/handlers_stats.go

@@ -18,10 +18,9 @@ func newStatsHandler(svc *service.StatsService) *statsHandler {
 }
 
 type statsCurrentResponse struct {
-	RunningCount     int32  `json:"running_count"`
-	VCPUsReserved    int32  `json:"vcpus_reserved"`
-	MemoryMBReserved int32  `json:"memory_mb_reserved"`
-	SampledAt        string `json:"sampled_at,omitempty"`
+	RunningCount     int32 `json:"running_count"`
+	VCPUsReserved    int32 `json:"vcpus_reserved"`
+	MemoryMBReserved int32 `json:"memory_mb_reserved"`
 }
 
 type statsPeaksResponse struct {
@@ -85,10 +84,6 @@ func (h *statsHandler) GetStats(w http.ResponseWriter, r *http.Request) {
 		},
 	}
 
-	if !current.SampledAt.IsZero() {
-		resp.Current.SampledAt = current.SampledAt.UTC().Format(time.RFC3339)
-	}
-
 	for i, pt := range series {
 		resp.Series.Labels[i] = pt.Bucket.UTC().Format(time.RFC3339)
 		resp.Series.Running[i] = pt.RunningCount