feat: implement n8n integration improvements and protocol version negotiation

- Add intelligent protocol version negotiation (2024-11-05 for n8n, 2025-03-26 for standard clients)
- Fix memory leak potential with async cleanup and connection close handling
- Enhance error sanitization for production environments
- Add schema validation for n8n nested output workaround
- Improve Docker security with unpredictable UIDs/GIDs
- Create n8n-friendly tool descriptions to reduce schema validation errors
- Add comprehensive protocol negotiation test suite

Addresses code review feedback:
- Protocol version inconsistency resolved
- Memory management improved
- Error information leakage fixed
- Docker security enhanced

🤖 Generated with [Claude Code](https://claude.ai/code)

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

src/mcp/workflow-examples.ts

@@ -0,0 +1,112 @@
+/**
+ * Example workflows for n8n AI agents to understand the structure
+ */
+
+export const MINIMAL_WORKFLOW_EXAMPLE = {
+  nodes: [
+    {
+      name: "Webhook",
+      type: "n8n-nodes-base.webhook",
+      typeVersion: 2,
+      position: [250, 300],
+      parameters: {
+        httpMethod: "POST",
+        path: "webhook"
+      }
+    }
+  ],
+  connections: {}
+};
+
+export const SIMPLE_WORKFLOW_EXAMPLE = {
+  nodes: [
+    {
+      name: "Webhook",
+      type: "n8n-nodes-base.webhook",
+      typeVersion: 2,
+      position: [250, 300],
+      parameters: {
+        httpMethod: "POST",
+        path: "webhook"
+      }
+    },
+    {
+      name: "Set",
+      type: "n8n-nodes-base.set",
+      typeVersion: 2,
+      position: [450, 300],
+      parameters: {
+        mode: "manual",
+        assignments: {
+          assignments: [
+            {
+              name: "message",
+              type: "string",
+              value: "Hello"
+            }
+          ]
+        }
+      }
+    },
+    {
+      name: "Respond to Webhook",
+      type: "n8n-nodes-base.respondToWebhook",
+      typeVersion: 1,
+      position: [650, 300],
+      parameters: {
+        respondWith: "firstIncomingItem"
+      }
+    }
+  ],
+  connections: {
+    "Webhook": {
+      "main": [
+        [
+          {
+            "node": "Set",
+            "type": "main",
+            "index": 0
+          }
+        ]
+      ]
+    },
+    "Set": {
+      "main": [
+        [
+          {
+            "node": "Respond to Webhook",
+            "type": "main",
+            "index": 0
+          }
+        ]
+      ]
+    }
+  }
+};
+
+export function getWorkflowExampleString(): string {
+  return `Example workflow structure:
+${JSON.stringify(MINIMAL_WORKFLOW_EXAMPLE, null, 2)}
+
+Each node MUST have:
+- name: unique string identifier
+- type: full node type with prefix (e.g., "n8n-nodes-base.webhook")
+- typeVersion: number (usually 1 or 2)
+- position: [x, y] coordinates array
+- parameters: object with node-specific settings
+
+Connections format:
+{
+  "SourceNodeName": {
+    "main": [
+      [
+        {
+          "node": "TargetNodeName",
+          "type": "main",
+          "index": 0
+        }
+      ]
+    ]
+  }
+}`;
+}