feat: add n8n integration with MCP Client Tool support

- Add N8N_MODE environment variable for n8n-specific behavior
- Implement HTTP Streamable transport with multiple session support
- Add protocol version endpoint (GET /mcp) for n8n compatibility
- Support multiple initialize requests for stateless n8n clients
- Add Docker configuration for n8n deployment
- Add test script with persistent volume support
- Add comprehensive unit tests for n8n mode
- Fix session management to handle per-request transport pattern

BREAKING CHANGE: Server now creates new transport for each initialize request
when running in n8n mode to support n8n's stateless client architecture

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

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

docker-compose.n8n.yml

@@ -0,0 +1,71 @@
+version: '3.8'
+
+services:
+  # n8n workflow automation
+  n8n:
+    image: n8nio/n8n:latest
+    container_name: n8n
+    restart: unless-stopped
+    ports:
+      - "${N8N_PORT:-5678}:5678"
+    environment:
+      - N8N_BASIC_AUTH_ACTIVE=${N8N_BASIC_AUTH_ACTIVE:-true}
+      - N8N_BASIC_AUTH_USER=${N8N_BASIC_AUTH_USER:-admin}
+      - N8N_BASIC_AUTH_PASSWORD=${N8N_BASIC_AUTH_PASSWORD:-password}
+      - N8N_HOST=${N8N_HOST:-localhost}
+      - N8N_PORT=5678
+      - N8N_PROTOCOL=${N8N_PROTOCOL:-http}
+      - WEBHOOK_URL=${N8N_WEBHOOK_URL:-http://localhost:5678/}
+      - N8N_ENCRYPTION_KEY=${N8N_ENCRYPTION_KEY}
+    volumes:
+      - n8n_data:/home/node/.n8n
+    networks:
+      - n8n-network
+    healthcheck:
+      test: ["CMD", "curl", "-f", "http://localhost:5678/healthz"]
+      interval: 30s
+      timeout: 10s
+      retries: 3
+      start_period: 30s
+
+  # n8n-mcp server for AI assistance
+  n8n-mcp:
+    build:
+      context: .
+      dockerfile: Dockerfile.n8n
+    image: ghcr.io/${GITHUB_REPOSITORY:-czlonkowski/n8n-mcp}/n8n-mcp:${VERSION:-latest}
+    container_name: n8n-mcp
+    restart: unless-stopped
+    ports:
+      - "${MCP_PORT:-3000}:3000"
+    environment:
+      - NODE_ENV=production
+      - N8N_MODE=true
+      - N8N_API_URL=http://n8n:5678
+      - N8N_API_KEY=${N8N_API_KEY}
+      - MCP_AUTH_TOKEN=${MCP_AUTH_TOKEN}
+      - LOG_LEVEL=${LOG_LEVEL:-info}
+    volumes:
+      - ./data:/app/data:ro
+      - mcp_logs:/app/logs
+    networks:
+      - n8n-network
+    depends_on:
+      n8n:
+        condition: service_healthy
+    healthcheck:
+      test: ["CMD", "curl", "-f", "http://localhost:3000/health"]
+      interval: 30s
+      timeout: 10s
+      retries: 3
+      start_period: 40s
+
+volumes:
+  n8n_data:
+    driver: local
+  mcp_logs:
+    driver: local
+
+networks:
+  n8n-network:
+    driver: bridge