feat(webui): show GPU serial in NVIDIA selection pickers

Every GPU-selection picker (Load/SAT, Burn, Benchmark) now renders the
card serial: "GPU N — <model> · <mem> MiB · sn: <serial>". The serial is
monospace and the digits that differ across the listed GPUs (common
prefix/suffix stripped) are emphasised so operators can tell cards apart.

Row markup was duplicated across three pages (and twice within
page_validate.go). Consolidated into a single module,
internal/webui/gpu_picker.go: beeGpuPicker.render({...}) builds every row;
gpuPickerCSS/gpuPickerJS are injected once by layoutHead/renderPage. Pages
keep their own selection-note text and multi-GPU toggles but no longer
hand-build <label> markup.

ListNvidiaGPUs() adds the serial via nvidia-smi --query-gpu=...,serial;
N/A is normalised to empty. Serial flows to the client unchanged through
the existing /api/gpu/nvidia JSON response.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01AudE3Q2nd9kxxVuxPKcTho

audit/internal/webui/page_burn.go

@@ -92,8 +92,6 @@ func renderBurn() string {
 .cb-row input[type=checkbox]:disabled { opacity:0.4; cursor:not-allowed; }
 .cb-row input[type=checkbox]:disabled ~ span { opacity:0.45; cursor:not-allowed; }
 .cb-note { font-size:11px; color:var(--muted); font-style:italic; }
-.burn-gpu-row { display:flex; align-items:flex-start; gap:8px; padding:6px 0; cursor:pointer; font-size:13px; }
-.burn-gpu-row input[type=checkbox] { width:16px; height:16px; margin-top:2px; flex-shrink:0; }
 .burn-profile-body { display:grid; grid-template-columns:1fr 1fr 1fr; gap:24px; align-items:stretch; }
 .burn-profile-col { min-width:0; }
 .burn-profile-action { display:flex; flex-direction:column; align-items:center; justify-content:flex-start; gap:8px; }
@@ -159,21 +157,11 @@ function burnUpdateSelectionNote() {
   note.textContent = 'Selected NVIDIA GPUs: ' + selected.join(', ') + '. Official and custom NVIDIA tasks will use only these GPUs.';
 }
 function burnRenderGPUList(gpus) {
-  const root = document.getElementById('burn-gpu-list');
-  if (!gpus || !gpus.length) {
-    root.innerHTML = '<p style="color:var(--muted);font-size:13px">No NVIDIA GPUs detected.</p>';
-    burnUpdateSelectionNote();
-    return;
-  }
-  root.innerHTML = gpus.map(function(gpu) {
-    const mem = gpu.memory_mb > 0 ? ' · ' + gpu.memory_mb + ' MiB' : '';
-    return '<label class="burn-gpu-row">'
-      + '<input class="burn-gpu-checkbox" type="checkbox" value="' + gpu.index + '" checked onchange="burnUpdateSelectionNote()">'
-      + '<span><strong>GPU ' + gpu.index + '</strong> — ' + gpu.name + mem + '</span>'
-      + '</label>';
-  }).join('');
-  burnApplyMultiGPUState(gpus.length);
-  burnUpdateSelectionNote();
+  beeGpuPicker.render({
+    rootId: 'burn-gpu-list', gpus: gpus,
+    checkboxClass: 'burn-gpu-checkbox', onToggle: 'burnUpdateSelectionNote()',
+    after: function(n) { burnApplyMultiGPUState(n); burnUpdateSelectionNote(); },
+  });
 }
 function burnSelectAll() {
   document.querySelectorAll('.burn-gpu-checkbox').forEach(function(el) { el.checked = true; });