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/devenv.nix

@@ -0,0 +1,66 @@
+{ pkgs, ... }: {
+  packages = with pkgs; [
+    # Node.js and package managers
+    nodejs_20
+    yarn
+    nodePackages.typescript
+    nodePackages.typescript-language-server
+
+    # Database
+    postgresql_15
+
+    # Development tools
+    git
+    curl
+    jq
+
+    # Optional: Add Docker if you want to manage Docker services
+    # docker
+    # docker-compose
+  ];
+
+  # PostgreSQL service for local development
+  services.postgres = {
+    enable = true;
+    package = pkgs.postgresql_15;
+    initialDatabases = [{ name = "website_monitoring"; }];
+    initialScript = ''
+      CREATE USER website_monitoring WITH PASSWORD 'password';
+      GRANT ALL PRIVILEGES ON DATABASE website_monitoring TO website_monitoring;
+    '';
+  };
+
+  # Optional: Add Redis if needed for caching/sessions
+  # services.redis.enable = true;
+
+  # Environment variables
+  env.POSTGRES_DB = "website_monitoring";
+  env.POSTGRES_USER = "website_monitoring";
+  env.POSTGRES_PASSWORD = "password";
+  env.DATABASE_URL = "postgresql://website_monitoring:password@localhost:5432/website_monitoring";
+
+  # Scripts that run when entering the environment
+  enterShell = ''
+    echo "🚀 Website Monitoring Frontend Development Environment"
+    echo "📦 Node.js $(node --version)"
+    echo "🐘 PostgreSQL $(psql --version)"
+    echo ""
+    echo "Available commands:"
+    echo "  npm run dev     - Start development server"
+    echo "  npm run build   - Build for production"
+    echo "  npm run lint    - Run ESLint"
+    echo "  psql            - Connect to PostgreSQL"
+    echo ""
+    echo "Database connection:"
+    echo "  Host: localhost"
+    echo "  Port: 5432"
+    echo "  Database: website_monitoring"
+    echo "  User: website_monitoring"
+    echo "  Password: password"
+    echo ""
+  '';
+
+  # Pre-commit hooks (optional)
+  # pre-commit.hooks.shellcheck.enable = true;
+  # pre-commit.hooks.nixpkgs-fmt.enable = true;
+}