fix(dashboard): let CSV exports use query cache instead of always force-querying

Two bugs caused dashboard CSV exports to always re-execute the query instead
of using the cache (while the Explore page correctly used the cache):

1. Chart.tsx passed `force: true` to `exportChart()`, unconditionally
   bypassing the cache on every dashboard export.

2. buildQuery.ts coerced a missing `row_limit` to `0` via `|| 0` for
   download queries, while display queries left it as `undefined`. This
   produced a different cache key so exports would miss the cache even
   without the `force` flag.

Both fixes are needed together: removing `force: true` lets the backend
consult the cache, and preserving `undefined` for a missing row_limit
ensures the export query produces the same cache key as the display query
that populated the cache.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

superset-frontend/plugins/plugin-chart-table/src/buildQuery.ts

@@ -227,7 +227,10 @@ export const buildQuery: BuildQuery<TableChartFormData> = (
         formData?.result_type === 'results');
 
     if (isDownloadQuery) {
-      moreProps.row_limit = Number(formDataCopy.row_limit) || 0;
+      moreProps.row_limit =
+        formDataCopy.row_limit != null
+          ? Number(formDataCopy.row_limit)
+          : undefined;
       moreProps.row_offset = 0;
     }
 

superset-frontend/src/dashboard/components/gridComponents/Chart/Chart.tsx

@@ -562,7 +562,6 @@ const Chart = (props: ChartProps) => {
             exportFormData as unknown as import('@superset-ui/core').QueryFormData,
           resultType,
           resultFormat: format,
-          force: true,
           ownState: exportOwnState,
           onStartStreamingExport: shouldUseStreaming
             ? (exportParams: JsonObject) => {