fix(traefik): request chart redraws once the dashboard has placed it, and refreshes every 5 min (#5214)

A chart built while its cell was still being laid out could stay blank until
a window resize; it now measures and draws again after layout settles. Each
refresh rebuilds the chart (the flash), and its buckets are minutes wide, so
the widget refreshes every 5 minutes instead of every poll.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

plugins/traefik/templates/traefik/widget_request_chart.html

@@ -30,7 +30,7 @@
     var hhmm = function (ms) {
       return new Date(ms).toLocaleTimeString([], { hour: "2-digit", minute: "2-digit" });
     };
-    new Chart(ctx.getContext("2d"), {
+    var chart = new Chart(ctx.getContext("2d"), {
       type: "line",
       data: {
         labels: times,
@@ -83,6 +83,14 @@
         }
       }
     });
+    // The chart is built while the dashboard may still be placing this cell,
+    // and a chart sized then can stay blank until a window resize (#5214).
+    // Measure and draw again once layout has settled.
+    setTimeout(function () {
+      if (!ctx.isConnected) return;
+      chart.resize();
+      chart.update("none");
+    }, 250);
   } catch (err) {
     fail(err && err.message ? err.message : String(err));
   }

steward/core/widgets.py

@@ -131,6 +131,7 @@ WIDGET_REGISTRY: dict[str, dict] = {
         "detail_url": "/plugins/traefik/",
         "plugin": "traefik",
         "poll": True,
+        "poll_seconds": 300,        # buckets are minutes wide; each refresh redraws the chart
         "params": [
             {
                 "key": "hours",