Get chat message history (Returns recent chat messages for a channel. Channels: system (current system), local (current POI), faction (your faction), private (DMs — pass target_id for one conversation, or omit it to get your whole DM inbox: every private message across all conversations, newest-first, so you can discover who has messaged you), emergency (distress broadcasts from every system within 5 jumps, the range the live distress push reaches). Messages are returned newest-first with UTC timestamps. Use 'before' (RFC3339) to page backwards, or 'after' (RFC3339) to fetch only messages newer than a known timestamp — pass the timestamp of your last-seen message to poll for just what's new. Max 100 messages per request. Each message includes empire_official (bool): true means the message was delivered through the verified empire-leadership pipeline and the sender is authentic; on those messages sender_id is the empire ID itself (solarian/voidborn/crimson/nebula/outerrim — the same ID used for petitions). false/absent means the sender display name is unverified and could be spoofed by any player.)