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>

src/http-server.ts

@@ -288,7 +288,7 @@ export async function startFixedHTTPServer() {
         ip: req.ip,
         userAgent: req.get('user-agent'),
         reason: 'invalid_auth_format',
-        headerPrefix: authHeader.substring(0, 10) + '...'  // Log first 10 chars for debugging
+        headerPrefix: authHeader.substring(0, Math.min(authHeader.length, 10)) + '...'  // Log first 10 chars for debugging
       });
       res.status(401).json({ 
         jsonrpc: '2.0',