fix(dashboard): add cache-busting and defensive chartManager guards to fix empty charts

static/js/pages/analytics.js

@@ -50,6 +50,14 @@ class AnalyticsPage {
     }
 
     async loadCharts() {
+        const cm = window.chartManager || await window.waitForChartManager();
+        if (!cm) {
+            this.showEmptyChart('analytics-chart', 'Chart system unavailable');
+            this.showEmptyChart('clients-chart', 'Chart system unavailable');
+            this.showEmptyChart('models-chart', 'Chart system unavailable');
+            return;
+        }
+
         // Fetch each data source independently so one failure doesn't kill the others
         const [timeSeriesResult, breakdownResult] = await Promise.allSettled([
             window.api.get('/usage/time-series'),
@@ -111,6 +119,8 @@ class AnalyticsPage {
     }
 
     renderAnalyticsChart(series) {
+        const cm = window.chartManager;
+        if (!cm) return;
         const data = {
             labels: series.map(s => s.time),
             datasets: [
@@ -130,10 +140,12 @@ class AnalyticsPage {
             ]
         };
         
-        window.chartManager.createLineChart('analytics-chart', data);
+        cm.createLineChart('analytics-chart', data);
     }
 
     renderClientsChart(clients) {
+        const cm = window.chartManager;
+        if (!cm) return;
         const data = {
             labels: clients.map(c => c.label),
             datasets: [{
@@ -143,17 +155,19 @@ class AnalyticsPage {
             }]
         };
         
-        window.chartManager.createHorizontalBarChart('clients-chart', data);
+        cm.createHorizontalBarChart('clients-chart', data);
     }
 
     renderModelsChart(models) {
+        const cm = window.chartManager;
+        if (!cm) return;
         const data = {
             labels: models.map(m => m.label),
             data: models.map(m => m.value),
-            colors: window.chartManager.defaultColors
+            colors: cm.defaultColors
         };
         
-        window.chartManager.createDoughnutChart('models-chart', data);
+        cm.createDoughnutChart('models-chart', data);
     }
 
     async loadUsageData() {