refactor(frontend): finish shadcn→custom primitive migration (green build)

- Remove tw-animate-css import + dead src/components/ui shadcn tree
- Convert 7 orphaned components (moderation, analysis, guild-selector,
  voice/activity-timeline, shared/empty+error) to new primitives
- Add missing moderation/view.tsx; analysis uses SearchPanel directly
- globals.css now uses new signal-driven ops-console tokens
- tsc --noEmit clean, next build green (11 routes), local smoke 200

services/frontend/src/components/primitives/skeleton.tsx

@@ -0,0 +1,20 @@
+import { cn } from "@/lib/utils";
+
+export interface SkeletonProps {
+  className?: string;
+  rounded?: boolean;
+}
+
+export function Skeleton({ className, rounded }: SkeletonProps) {
+  return (
+    <div
+      aria-hidden
+      className={cn(
+        "animate-shimmer rounded-[var(--radius-r-control)]",
+        "bg-[var(--color-surface-2)]",
+        rounded && "rounded-full",
+        className,
+      )}
+    />
+  );
+}