Initial commit: React frontend (SLP Software) + AIDLC workflow docs

Co-authored-by: Junie <junie@jetbrains.com>

src/components/ErrorBoundary.tsx

@@ -0,0 +1,42 @@
+import { Component } from 'react';
+import type { ErrorInfo, ReactNode } from 'react';
+
+interface ErrorBoundaryProps {
+  children: ReactNode;
+}
+
+interface ErrorBoundaryState {
+  hasError: boolean;
+}
+
+/**
+ * Top-level, on-brand error boundary (NFR Design resilience pattern; SECURITY-09/SECURITY-15).
+ * Shows a generic, themed fallback message — never technical details like stack traces.
+ */
+export class ErrorBoundary extends Component<ErrorBoundaryProps, ErrorBoundaryState> {
+  state: ErrorBoundaryState = { hasError: false };
+
+  static getDerivedStateFromError(): ErrorBoundaryState {
+    return { hasError: true };
+  }
+
+  componentDidCatch(error: Error, info: ErrorInfo): void {
+    console.error('Unexpected application error', error, info);
+  }
+
+  render(): ReactNode {
+    if (this.state.hasError) {
+      return (
+        <div
+          className="theme-red flex min-h-screen items-center justify-center bg-bg px-6 text-center text-text"
+          role="alert"
+          data-testid="error-boundary-fallback"
+        >
+          <p className="font-display text-lg">Er ging iets mis. Probeer de pagina te vernieuwen.</p>
+        </div>
+      );
+    }
+
+    return this.props.children;
+  }
+}