fix(web): remove dashboard loading.tsx to eliminate double skeleton flash

The route-level loading.tsx creates a Suspense boundary that shows a
generic skeleton on every page navigation within the dashboard. Since
every page already handles its own data-loading skeleton via TanStack
Query isLoading, this causes two sequential skeleton flashes:
loading.tsx skeleton → page skeleton → content.

Removing it makes the old page stay visible during route transitions
(typically <100ms), then the new page renders directly with its own
skeleton — a single, smooth transition.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

apps/web/app/[workspaceSlug]/(dashboard)/loading.tsx

@@ -1,28 +0,0 @@
-import { Skeleton } from "@multica/ui/components/ui/skeleton";
-
-export default function DashboardLoading() {
-  return (
-    <div className="flex flex-1 min-h-0 flex-col">
-      {/* Header skeleton */}
-      <div className="flex h-12 shrink-0 items-center gap-2 border-b px-4">
-        <Skeleton className="h-5 w-5 rounded" />
-        <Skeleton className="h-4 w-32" />
-      </div>
-      {/* Toolbar skeleton */}
-      <div className="flex h-12 shrink-0 items-center justify-between border-b px-4">
-        <Skeleton className="h-5 w-24" />
-        <Skeleton className="h-8 w-24" />
-      </div>
-      {/* Content skeleton */}
-      <div className="flex-1 p-4 space-y-3">
-        {Array.from({ length: 6 }).map((_, i) => (
-          <div key={i} className="flex items-center gap-3">
-            <Skeleton className="h-4 w-4 rounded" />
-            <Skeleton className="h-4 flex-1 max-w-md" />
-            <Skeleton className="h-4 w-16" />
-          </div>
-        ))}
-      </div>
-    </div>
-  );
-}