fix: memory leak in session removal - close MCP server properly (#471) (#472)

- Add close() method to N8NDocumentationMCPServer that:
  - Calls server.close() (MCP SDK cleanup)
  - Clears internal cache
  - Nullifies service references to help GC
- Update removeSession() to call server.close() before releasing references

Root cause: removeSession() deleted server from map but didn't call cleanup
Evidence: Production server memory grew ~1GB in 43 minutes (10% to 35%)

Conceived by Romuald Członkowski - https://www.aiadvisors.pl/en

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

Co-authored-by: Romuald Członkowski <romualdczlonkowski@MacBook-Pro-Romuald.local>
Co-authored-by: Claude <noreply@anthropic.com>

dist/http-server-single-session.js

@@ -101,10 +101,14 @@ class SingleSessionHTTPServer {
     async removeSession(sessionId, reason) {
         try {
             const transport = this.transports[sessionId];
+            const server = this.servers[sessionId];
             delete this.transports[sessionId];
             delete this.servers[sessionId];
             delete this.sessionMetadata[sessionId];
             delete this.sessionContexts[sessionId];
+            if (server) {
+                await server.close();
+            }
             if (transport) {
                 await transport.close();
             }