BrokerMessageTypes

Broker-app extensions to MessageTypes. The upstream enum owns ordinals up to ConnectionRestored; we allocate from 10000+ (FIX-style user-defined range) so a future upstream addition cannot collide with our values regardless of how many entries it appends. Constants are typed as MessageTypes so a broker-app message subclass can pass them straight to base(MessageTypes) without any cast at the call site. Add new entries here (not in per-module files) so every server module sees the same canonical list.