feat(ui): add loading transition and TreeSpinner to drill-down

- Show opacity transition on groups table when drilling down
- Use TreeSpinner with "Loading resources..." text in drill-down view
- Match provider wizard spinner style with button-primary color

Ref: PROWLER-881

ui/components/findings/table/findings-group-drill-down.tsx

@@ -7,7 +7,7 @@ import {
   RowSelectionState,
   useReactTable,
 } from "@tanstack/react-table";
-import { ChevronLeft, Loader2 } from "lucide-react";
+import { ChevronLeft } from "lucide-react";
 import { useRouter, useSearchParams } from "next/navigation";
 import { useCallback, useMemo, useState } from "react";
 
@@ -20,6 +20,7 @@ import {
   TableRow,
 } from "@/components/ui/table";
 import { SeverityBadge, StatusFindingBadge } from "@/components/ui/table";
+import { TreeSpinner } from "@/components/shadcn/tree-view/tree-spinner";
 import { useInfiniteResources } from "@/hooks/use-infinite-resources";
 import { cn, hasDateOrScanFilter } from "@/lib";
 import { FindingGroupRow, FindingResourceRow } from "@/types";
@@ -250,8 +251,11 @@ export function FindingsGroupDrillDown({
 
           {/* Loading indicator */}
           {isLoading && (
-            <div className="flex items-center justify-center py-8">
-              <Loader2 className="text-text-neutral-tertiary size-6 animate-spin" />
+            <div className="flex items-center justify-center gap-2 py-8">
+              <TreeSpinner className="size-6" />
+              <span className="text-text-neutral-tertiary text-sm">
+                Loading resources...
+              </span>
             </div>
           )}
 

ui/components/findings/table/findings-group-table.tsx

@@ -27,6 +27,7 @@ export function FindingsGroupTable({
   const [expandedGroup, setExpandedGroup] = useState<FindingGroupRow | null>(
     null,
   );
+  const [isDrillingDown, setIsDrillingDown] = useState(false);
 
   // Track finding group IDs to detect data changes (e.g., after muting)
   const currentIds = (data ?? []).map((g) => g.id).join(",");
@@ -82,9 +83,14 @@ export function FindingsGroupTable({
   };
 
   const handleDrillDown = (checkId: string, group: FindingGroupRow) => {
-    setExpandedCheckId(checkId);
-    setExpandedGroup(group);
+    setIsDrillingDown(true);
     setRowSelection({});
+    // Brief loading state before switching to drill-down view
+    setTimeout(() => {
+      setExpandedCheckId(checkId);
+      setExpandedGroup(group);
+      setIsDrillingDown(false);
+    }, 150);
   };
 
   const handleCollapse = () => {
@@ -128,6 +134,7 @@ export function FindingsGroupTable({
         getRowCanSelect={getRowCanSelect}
         showSearch
         searchPlaceholder="Search by Check ID"
+        isLoading={isDrillingDown}
       />
 
       {selectedFindingIds.length > 0 && (