fix(webui): prevent orphaned workers on restart, reduce metrics polling, add Kill Workers button

- tasks: mark TaskRunning tasks as TaskFailed on bee-web restart instead of
  re-queueing them — prevents duplicate gpu-burn-worker spawns when bee-web
  crashes mid-test (each restart was launching a new set of 8 workers on top
  of still-alive orphans from the previous crash)
- server: reduce metrics collector interval 1s→5s, grow ring buffer to 360
  samples (30 min); cuts nvidia-smi/ipmitool/sensors subprocess rate by 5×
- platform: add KillTestWorkers() — scans /proc and SIGKILLs bee-gpu-burn,
  stress-ng, stressapptest, memtester without relying on pkill/killall
- webui: add "Kill Workers" button next to Cancel All; calls
  POST /api/tasks/kill-workers which cancels the task queue then kills
  orphaned OS-level processes; shows toast with killed count
- metricsdb: sort GPU indices and fan/temp names after map iteration to fix
  non-deterministic sample reconstruction order (flaky test)
- server: fix chartYAxisNumber to use one decimal place for 1000–9999
  (e.g. "1,7к" instead of "2к") so Y-axis ticks are distinguishable

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

audit/internal/webui/tasks.go

@@ -716,6 +716,38 @@ func (h *handler) handleAPITasksCancelAll(w http.ResponseWriter, _ *http.Request
 	writeJSON(w, map[string]int{"cancelled": n})
 }
 
+func (h *handler) handleAPITasksKillWorkers(w http.ResponseWriter, _ *http.Request) {
+	// Cancel all queued/running tasks in the queue first.
+	globalQueue.mu.Lock()
+	now := time.Now()
+	cancelled := 0
+	for _, t := range globalQueue.tasks {
+		switch t.Status {
+		case TaskPending:
+			t.Status = TaskCancelled
+			t.DoneAt = &now
+			cancelled++
+		case TaskRunning:
+			if t.job != nil {
+				t.job.abort()
+			}
+			t.Status = TaskCancelled
+			t.DoneAt = &now
+			cancelled++
+		}
+	}
+	globalQueue.persistLocked()
+	globalQueue.mu.Unlock()
+
+	// Kill orphaned test worker processes at the OS level.
+	killed := platform.KillTestWorkers()
+	writeJSON(w, map[string]any{
+		"cancelled": cancelled,
+		"killed":    len(killed),
+		"processes": killed,
+	})
+}
+
 func (h *handler) handleAPITasksStream(w http.ResponseWriter, r *http.Request) {
 	id := r.PathValue("id")
 	// Wait up to 5s for the task to get a job (it may be pending)
@@ -769,8 +801,17 @@ func (q *taskQueue) loadLocked() {
 			params:    pt.Params,
 		}
 		q.assignTaskLogPathLocked(t)
-		if t.Status == TaskPending || t.Status == TaskRunning {
-			t.Status = TaskPending
+		if t.Status == TaskRunning {
+			// The task was interrupted by a bee-web restart. Child processes
+			// (e.g. bee-gpu-burn-worker) survive the restart in their own
+			// process groups and cannot be cancelled retroactively. Mark the
+			// task as failed so the user can decide whether to re-run it
+			// rather than blindly re-launching duplicate workers.
+			now := time.Now()
+			t.Status = TaskFailed
+			t.DoneAt = &now
+			t.ErrMsg = "interrupted by bee-web restart"
+		} else if t.Status == TaskPending {
 			t.StartedAt = nil
 			t.DoneAt = nil
 			t.ErrMsg = ""