fix(BIZ-42): critical deadlock + major review issues

- Fix #1 (Critical): evaluate_retreat() deadlock — changed _retreat_lock to
  threading.RLock() to allow reentrant acquisition when evaluate_retreat()
  calls get_429_rate() while holding the lock
- Fix #2 (Major): Dashboard queue chart now uses snap.queue.per_priority
  instead of Math.random() mock data
- Fix #3 (Major): structlog uses JSONRenderer instead of ConsoleRenderer
  for JSON-format output as required by acceptance criteria
- Bonus: webui.py _build_snapshot() now async and includes queue data
  with per-priority depth for dashboard consumption

Reviewed-by: 梁思筑 (architect)
Co-authored-by: multica-agent <github@multica.ai>

services/nvidia_sidecar/static/dashboard.html

@@ -186,12 +186,13 @@ function updateDashboard(snap) {
   ];
   chartTokens.update();
 
-  const mb = (snap.metrics_buffer || {});
+  const qs = snap.queue || {};
+  const perPriority = qs.per_priority || {};
   chartQueue.data.datasets[0].data = [
-    Math.round(Math.random() * 5),
-    Math.round(Math.random() * 10),
-    Math.round(Math.random() * 15),
-    Math.round(Math.random() * 20)
+    perPriority.URGENT || 0,
+    perPriority.HIGH || 0,
+    perPriority.NORMAL || 0,
+    perPriority.LOW || 0
   ];
   chartQueue.update();