feat(monitor): explain why a query failed (port not listening vs. no reply) #4995

Problem

When a monitor query fails, the log only says the query failed and the server is restarted. Admins can't tell why. Common causes include:

• The server never opened the query port (it didn't finish booting, or another program already holds a port it needs).
• Something is listening on the port but doesn't answer the query, for example because queryport is wrong or the query type/protocol doesn't match.

Proposal

After a failed query attempt, check the port with ss and log a hint:

• Port not in use: the server isn't listening on queryport. Check the console, port settings and port conflicts.
• Port in use: name the process listening on it. If the query got no reply, suggest checking queryport and the query mode/type.

Hints should go to the script log (fn_script_log_*) as well as the screen, so they appear in the monitor log.

Originally proposed by @jusito in #4155 (closed, written against the pre-lgsm/modules monitor).