Players lose their private conversations on reconnect or on another
device. Servatrice can already log private messages, but only
moderators can read the logs.
Add Command_GetPrivateChatHistory / Response_PrivateChatHistory so a
registered user can page through their own logged conversation with one
other user. Operators opt in with logging/allow_user_chat_history
(default off, and log_user_msg_chat must be on). The caller is matched
by account id so reused guest or deleted-account names can't read older
messages; only time, sender name and text are returned. Pages hold
1..200 messages and never split a second, since log_time has 1-second
resolution.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
