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/pages.go

@@ -1577,8 +1577,10 @@ func renderInstall() string {
 // ── Tasks ─────────────────────────────────────────────────────────────────────
 
 func renderTasks() string {
-	return `<div style="display:flex;align-items:center;gap:12px;margin-bottom:16px">
+	return `<div style="display:flex;align-items:center;gap:12px;margin-bottom:16px;flex-wrap:wrap">
 <button class="btn btn-danger btn-sm" onclick="cancelAll()">Cancel All</button>
+<button class="btn btn-sm" style="background:#b45309;color:#fff" onclick="killWorkers()" title="Send SIGKILL to all running test processes (bee-gpu-burn, stress-ng, stressapptest, memtester)">Kill Workers</button>
+<span id="kill-toast" style="font-size:12px;color:var(--muted);display:none"></span>
 <span style="font-size:12px;color:var(--muted)">Tasks run one at a time. Logs persist after navigation.</span>
 </div>
 <div class="card">
@@ -1639,6 +1641,21 @@ function cancelTask(id) {
 function cancelAll() {
   fetch('/api/tasks/cancel-all',{method:'POST'}).then(()=>loadTasks());
 }
+function killWorkers() {
+  if (!confirm('Send SIGKILL to all running test workers (bee-gpu-burn, stress-ng, stressapptest, memtester)?\n\nThis will also cancel all queued and running tasks.')) return;
+  fetch('/api/tasks/kill-workers',{method:'POST'})
+    .then(r=>r.json())
+    .then(d=>{
+      loadTasks();
+      var toast = document.getElementById('kill-toast');
+      var parts = [];
+      if (d.cancelled > 0) parts.push(d.cancelled+' task'+(d.cancelled===1?'':'s')+' cancelled');
+      if (d.killed > 0) parts.push(d.killed+' process'+(d.killed===1?'':'es')+' killed');
+      toast.textContent = parts.length ? parts.join(', ')+'.' : 'No processes found.';
+      toast.style.display = '';
+      setTimeout(()=>{ toast.style.display='none'; }, 5000);
+    });
+}
 function setPriority(id, delta) {
   fetch('/api/tasks/'+id+'/priority',{method:'POST',headers:{'Content-Type':'application/json'},body:JSON.stringify({delta:delta})})
     .then(()=>loadTasks());