Relax Node prerequisite to 18+

The quickstart uses only the Anthropic SDK and process.env — none of the
recent Node APIs that would require a higher floor.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

Author: AnnaXWang

integrations/claude-managed-agents.mdx

@@ -39,7 +39,7 @@ Inside a session, the agent uses its built-in shell to run the Kernel CLI — e.
 
 ## Prerequisites
 
-- **Node.js 22+** and the [Anthropic TypeScript SDK](https://github.com/anthropics/anthropic-sdk-typescript) (`@anthropic-ai/sdk`).
+- **Node.js 18+** and the [Anthropic TypeScript SDK](https://github.com/anthropics/anthropic-sdk-typescript) (`@anthropic-ai/sdk`).
 - **ANTHROPIC_API_KEY**: get from the [Anthropic Console](https://console.anthropic.com/). Drives vaults, agents, and sessions.
 - **KERNEL_API_KEY**: get from the [Kernel Dashboard](https://dashboard.onkernel.com/api-keys). Stored in the vault and injected into the sandbox as a placeholder.
 - Early-access enrollment in Claude Managed Agents (including the `environment_variable` vault credential feature).