feat(02-03): update DashboardSkeleton for 3-column chart layout

- Replace 2-column chart skeleton with 3-column grid (md:grid-cols-2 lg:grid-cols-3)
- Add third skeleton chart card matching real donut/bar/bar layout
- Update skeleton height to 250px to match chart component heights

src/components/dashboard/DashboardSkeleton.tsx

@@ -25,14 +25,14 @@ export function DashboardSkeleton() {
         <SkeletonStatCard />
       </div>
 
-      {/* Chart area skeleton */}
+      {/* 3-column chart area skeleton */}
-      <div className="grid gap-6 lg:grid-cols-2">
+      <div className="grid gap-6 md:grid-cols-2 lg:grid-cols-3">
         <Card>
           <CardHeader>
             <Skeleton className="h-5 w-40" />
           </CardHeader>
           <CardContent>
-            <Skeleton className="h-[240px] w-full rounded-md" />
+            <Skeleton className="h-[250px] w-full rounded-md" />
           </CardContent>
         </Card>
         <Card>
@@ -40,7 +40,15 @@ export function DashboardSkeleton() {
             <Skeleton className="h-5 w-40" />
           </CardHeader>
           <CardContent>
-            <Skeleton className="h-[240px] w-full rounded-md" />
+            <Skeleton className="h-[250px] w-full rounded-md" />
+          </CardContent>
+        </Card>
+        <Card>
+          <CardHeader>
+            <Skeleton className="h-5 w-40" />
+          </CardHeader>
+          <CardContent>
+            <Skeleton className="h-[250px] w-full rounded-md" />
           </CardContent>
         </Card>
       </div>