CONF-021: initialize answers an unsupported version with a supported one

Severity	Applies to	Spec section
warn	legacy era, stdio, http	2025-11-25/basic/lifecycle#version-negotiation

Sends initialize asking for version 1900-01-01 on a fresh session. If the server does not support the requested version it MUST respond with another protocol version it supports, so the client can decide whether to continue. The same page's error-handling example answers with a -32602 error instead, so an error is reported as a warning, not a failure.

From the command line: mcpprobe checks explain CONF-021. To leave it out of a run, add "CONF-021" to [checks] disable in mcpprobe.toml; to change how much it counts, use severity_overrides.