refactor: flatten monorepo structure to backend/ frontend/ devops/

Rename subdirectories for a cleaner single-repo layout:
- website-monitoring-backend/  → backend/
- website-monitoring-frontend/ → frontend/
- website-monitoring-devops/   → devops/

Update all references in package.json scripts, CI workflows,
docker-compose, pre-commit hooks, and documentation.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

frontend/src/app/providers.tsx

@@ -0,0 +1,12 @@
+"use client";
+
+import { AuthProvider } from "@/contexts/AuthContext";
+import { ErrorBoundary } from "@/components/ui/feedback/ErrorBoundary";
+
+export function Providers({ children }: { children: React.ReactNode }) {
+  return (
+    <AuthProvider>
+      <ErrorBoundary>{children}</ErrorBoundary>
+    </AuthProvider>
+  );
+}