feat: add error boundary, glass shimmer skeleton, empty state

- Create ErrorBoundary class component with GlassCard fallback UI
- Update LoadingSkeleton with glass shimmer animation overlay
- Update EmptyState with GlassPanel and default Inbox icon
- Add ErrorBoundary to shared components index export

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

services/frontend/src/components/shared/error-boundary.tsx

@@ -0,0 +1,35 @@
+"use client";
+
+import { Component, type ReactNode } from "react";
+import { GlassCard } from "@/components/glass/card";
+import { AlertCircle, RefreshCw } from "lucide-react";
+
+interface Props { children: ReactNode; fallback?: ReactNode; }
+interface State { hasError: boolean; error?: Error; }
+
+export class ErrorBoundary extends Component<Props, State> {
+  state: State = { hasError: false };
+
+  static getDerivedStateFromError(error: Error): State {
+    return { hasError: true, error };
+  }
+
+  render() {
+    if (this.state.hasError) {
+      return this.props.fallback || (
+        <GlassCard variant="danger" className="flex flex-col items-center gap-2 py-8">
+          <AlertCircle className="size-6 text-destructive" />
+          <p className="text-sm text-text-secondary">{this.state.error?.message || "Something went wrong"}</p>
+          <button
+            type="button"
+            onClick={() => this.setState({ hasError: false })}
+            className="flex items-center gap-1 text-xs text-primary hover:text-primary/80 transition-colors"
+          >
+            <RefreshCw className="size-3" /> Try again
+          </button>
+        </GlassCard>
+      );
+    }
+    return this.props.children;
+  }
+}