Fix forecast burndown chart data issues

- Fix Date object handling for resolution_date from PostgreSQL
- Fix totalAssets using per-metric summary (vcl_multi_vertical_summary)
  instead of vertical-level compliance_snapshots total_devices
- Fix duplicate current month in chart (forecast starts from next month)
- Fix multi-vertical metrics summing across all relevant verticals
- Fix bar stacking: orange (non-compliant) on bottom, blue (compliant)
  on top, both sharing same baseline (stacked to total)
- Add fill props to Bar components for correct legend colors
- Backfill historical snapshots with per-metric totalAssets

frontend/src/components/pages/CCPMetricsPage.js

@@ -1367,8 +1367,8 @@ function ForecastBurndownChart({ metricId }) {
 
     // Combine historical and forecast into a single array with isForecast flag
     const combinedData = [
-        ...historical.map(d => ({ ...d, isForecast: false })),
-        ...forecast.map(d => ({ ...d, isForecast: true })),
+        ...historical.map(d => ({ ...d, compliant: (d.total_assets || 0) - (d.non_compliant || 0), isForecast: false })),
+        ...forecast.map(d => ({ ...d, compliant: (d.total_assets || 0) - (d.non_compliant || 0), isForecast: true })),
     ];
 
     // Determine the divider position (between last historical and first forecast)
@@ -1399,11 +1399,12 @@ function ForecastBurndownChart({ metricId }) {
 
     // Custom label for bars (device counts inside bars)
     const renderTotalLabel = (props) => {
-        const { x, y, width, height, value } = props;
-        if (!value || height < 14) return null;
+        const { x, y, width, height, payload } = props;
+        const total = payload ? payload.total_assets : null;
+        if (!total || height < 14) return null;
         return (
             <text x={x + width / 2} y={y + height / 2} textAnchor="middle" dominantBaseline="middle" fill="#FFF" fontSize={9} fontWeight="600">
-                {value}
+                {total}
             </text>
         );
     };
@@ -1487,19 +1488,23 @@ function ForecastBurndownChart({ metricId }) {
                     )}
                     <Bar
                         yAxisId="left"
-                        dataKey="total_assets"
-                        name="Total Assets"
-                        shape={renderTotalAssetsBar}
-                        label={renderTotalLabel}
-                        barSize={28}
+                        dataKey="non_compliant"
+                        name="Non-Compliant"
+                        stackId="devices"
+                        fill="#F97316"
+                        shape={renderNonCompliantBar}
+                        label={renderNonCompliantLabel}
+                        barSize={36}
                     />
                     <Bar
                         yAxisId="left"
-                        dataKey="non_compliant"
-                        name="Non-Compliant"
-                        shape={renderNonCompliantBar}
-                        label={renderNonCompliantLabel}
-                        barSize={28}
+                        dataKey="compliant"
+                        name="Compliant"
+                        stackId="devices"
+                        fill="#3B82F6"
+                        shape={renderTotalAssetsBar}
+                        label={renderTotalLabel}
+                        barSize={36}
                     />
                     <Line
                         yAxisId="right"