All client-to-server commands now go through POST /api/v1/messages
with a 'command' field. The server dispatches by command type:
- PRIVMSG/NOTICE: send message to channel or user
- JOIN: join channel (creates if needed)
- PART: leave channel
- NICK: change nickname
- TOPIC: set channel topic
- PING: keepalive (returns PONG)
Removed separate routes:
- POST /channels/join
- DELETE /channels/{channel}
- POST /register (renamed to POST /session)
- GET /channels/all (moved to GET /channels)
Added DB methods: ChangeNick, SetTopic
- HandleState returns user info (id, nick) + joined channels in one response
- HandleGetMessages now serves unified message stream (was HandlePoll)
- HandleSendMessage accepts 'to' field for routing to #channel or nick
- HandleGetHistory supports scrollback for channels and DMs
- Remove separate HandleMe, HandleListChannels, HandleSendDM, HandleGetDMs, HandlePoll
