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>

Dockerfile.n8n

@@ -0,0 +1,75 @@
+# Multi-stage Dockerfile optimized for n8n integration
+# Stage 1: Build stage
+FROM node:20-alpine AS builder
+
+# Install build dependencies
+RUN apk add --no-cache python3 make g++ git
+
+# Set working directory
+WORKDIR /app
+
+# Copy package files
+COPY package*.json ./
+
+# Install all dependencies (including dev deps for building)
+RUN npm ci
+
+# Copy source code
+COPY . .
+
+# Build the application
+RUN npm run build
+
+# Stage 2: Production stage
+FROM node:20-alpine
+
+# Install runtime dependencies
+RUN apk add --no-cache \
+    curl \
+    tini \
+    && rm -rf /var/cache/apk/*
+
+# Create non-root user with less common UID/GID
+RUN addgroup -g 1001 n8n-mcp && \
+    adduser -u 1001 -G n8n-mcp -s /bin/sh -D n8n-mcp
+
+# Set working directory
+WORKDIR /app
+
+# Copy package files
+COPY package*.json ./
+
+# Install production dependencies only
+RUN npm ci --only=production && \
+    npm cache clean --force
+
+# Copy built application from builder stage
+COPY --from=builder /app/dist ./dist
+COPY --from=builder /app/data ./data
+
+# Create necessary directories and set permissions
+RUN mkdir -p /app/logs /app/data && \
+    chown -R n8n-mcp:n8n-mcp /app
+
+# Switch to non-root user
+USER n8n-mcp
+
+# Set environment variables for n8n mode
+ENV NODE_ENV=production \
+    N8N_MODE=true \
+    N8N_API_URL="" \
+    N8N_API_KEY="" \
+    PORT=3000
+
+# Expose port
+EXPOSE 3000
+
+# Health check
+HEALTHCHECK --interval=30s --timeout=10s --start-period=40s --retries=3 \
+    CMD curl -f http://localhost:${PORT}/health || exit 1
+
+# Use tini for proper signal handling
+ENTRYPOINT ["/sbin/tini", "--"]
+
+# Start the application in n8n mode
+CMD ["node", "dist/index.js", "n8n"]