fix(sidecar-v2): second-round review fixes

- cooldown_manager: move function-level imports to module top
- proxy.py: emergency_count counter now actually increments
- server.py: metrics reads emergency_count from proxy module
- dashboard.html: real JS CDN fallback (not just comment)
- requirements.txt: remove unused prometheus_client

Round 2 review residual fixes from 沈路明/陆怀瑾/梁思筑 feedback

Co-authored-by: multica-agent <github@multica.ai>

services/nvidia_sidecar/dashboard.html

@@ -4,9 +4,25 @@
 <meta charset="UTF-8">
 <meta name="viewport" content="width=device-width, initial-scale=1.0">
 <title>Sidecar V2 — Provider Pool Dashboard</title>
+<!-- Primary: jsDelivr CDN -->
 <script src="https://cdn.jsdelivr.net/npm/chart.js@4.4.0/dist/chart.umd.min.js"></script>
-<!-- CDN fallback: place chart.umd.min.js in static/ for offline deployments -->
-<script>if(typeof Chart==='undefined'){document.write('<script src="/static/chart.umd.min.js"><\/script>')}</script>
+<!-- Fallback: local static copy for offline/intranet deployments -->
+<script>
+(function() {
+  var check = function() {
+    if (typeof Chart === 'undefined') {
+      var s = document.createElement('script');
+      s.src = '/static/chart.umd.min.js';
+      s.onerror = function() {
+        console.warn('Chart.js unavailable (CDN + local both failed). Charts disabled.');
+      };
+      document.head.appendChild(s);
+    }
+  };
+  // Check after CDN script has had a chance to load
+  setTimeout(check, 2000);
+})();
+</script>
 <style>
   :root {
     --bg: #0f1117;