perf(cluster): dim spots via cell class, not redrawRows (0.23.6 slowdown)

The "dim spots that represent nothing" feature drove the dimming with getRowStyle
and called api.redrawRows() on EVERY spotStatus update to re-apply it — a full
grid re-render on a firehose of status updates, which pegged the CPU on a busy
cluster (reported as PCs slowing down since 0.23.6). Move the dimming to a
defaultColDef cellClassRules ('opacity-40') that the existing light
refreshCells({force:true}) re-applies; drop redrawRows and getRowStyle.

frontend/src/components/ClusterGrid.tsx

@@ -410,6 +410,11 @@ export function ClusterGrid({ rows, spotStatus, onSpotClick }: Props) {
 
   const defaultColDef = useMemo<ColDef>(() => ({
     sortable: true, resizable: true, filter: true, suppressMovable: false,
+    // Dim "represents nothing" spots at the CELL level, via a class that
+    // refreshCells re-applies. Doing it with a row STYLE needed redrawRows() on
+    // every status update, which re-rendered the whole grid continuously and
+    // pegged the CPU on a busy cluster (the 0.23.6 slowdown).
+    cellClassRules: { 'opacity-40': (p: any) => isDull(statusFor(p)) },
   }), []);
 
   // Pass spotStatus through AG Grid's context so cell renderers can look up
@@ -423,9 +428,10 @@ export function ClusterGrid({ rows, spotStatus, onSpotClick }: Props) {
   // won't re-render those cells on its own — force a refresh so e.g. a worked call
   // turns blue once its status loads.
   useEffect(() => {
-    // redrawRows (not refreshCells) so getRowStyle re-runs too — the whole-row
-    // dimming of "represents nothing" spots depends on the status that lands here.
-    gridRef.current?.api?.redrawRows();
+    // Light refresh so status-dependent styling — the Call/Band/Mode colours AND
+    // the dimmed "represents nothing" class (cellClassRules above) — re-applies
+    // once a status lands, WITHOUT redrawing whole rows (which pegged the CPU).
+    gridRef.current?.api?.refreshCells({ force: true });
   }, [spotStatus]);
 
   // Restore AFTER the profile scope is known — this grid has no key= remount to
@@ -511,7 +517,6 @@ export function ClusterGrid({ rows, spotStatus, onSpotClick }: Props) {
             onColumnVisible={saveColumnState}
             onSortChanged={saveColumnState}
             onRowClicked={handleRowClicked}
-            getRowStyle={(p: any) => (isDull(statusFor(p)) ? { opacity: 0.4 } : undefined)}
             animateRows={false}
             suppressCellFocus
             getRowId={(p) => `${(p.data as any).received_at}-${(p.data as any).dx_call}-${(p.data as any).source_id}`}