refactor: chat packets as structs

Every packet of the chat service is now an LUBitStream struct in dNet/ChatPackets.h
(docs/PacketArchitecture.md, PR 13), and nothing in the chat server or the chat side of
the world server reads or writes a packet by hand any more.

- World <-> chat: LoginSessionNotify, UnexpectedDisconnect, GMLevelUpdate, GMMute,
  Announcement (GM announce), CreateTeam, TeamUpdate (TEAM_GET_STATUS to worlds),
  AchievementNotify, ShowAllRequest, FindPlayerRequest.
- Client -> world -> chat (friends, ignore list, teams, general and private chat):
  GetFriendsList, AddFriendRequest, AddFriendResponse, RemoveFriend, GetIgnoreList,
  AddIgnore, RemoveIgnore, GeneralChatMessage, PrivateChatMessage, TeamInvite,
  TeamInviteResponse, TeamLeave, TeamKick, TeamSetLeader, TeamSetLoot, TeamGetStatus.
  The 77 bytes the handlers skipped are named fields now (the sender block the client
  fills in); the 4 unused bytes after the player ID are kept as `unknown`.
- What the client receives. Chat service (ChatPackets::Client): GeneralChatMessage
  (replaces SendChatMessage; SendSystemMessage stays as a helper built on it),
  PrivateChatMessage. Client service (ClientPackets, as structs go in the file of the
  ServiceType in their header): SendCannedText (replaces SendMessageFail), GetFriendsListResponse, AddFriendRequest,
  AddFriendResponse, RemoveFriendResponse, UpdateFriendNotify, WhoResponse,
  ShowAllResponse, Get/Add/RemoveIgnoreResponse, TeamInvite, TeamInviteInitialResponse,
  and the team game messages chat writes (TeamInviteConfirm, TeamGetStatusResponse,
  TeamSetLeader, TeamAddPlayer, TeamRemovePlayer, TeamSetOffWorldFlag) as TeamGameMsg
  structs, since chat doesn't link dGame's NetGameMsg.
- WORLD_ROUTE_PACKET is ChatPackets::WorldRoutePacket (its own file, dNet/WorldRoutePacket.h,
  since it carries packets of other services): the target and the inner packet.
  ChatPacketHandler::SendRouted replaces the per-function route headers and
  SendRoutedMsg.

Dispatch: dNet/PacketDispatcher.h is a dispatch map from packet ID to (struct, handler
function); packets that fail to Deserialize are logged and dropped. The chat server's
switch and the world's HandlePacketChat switch are now maps. The handlers take the
structs; their logic is unchanged. World code sends to chat with ChatServerLink::Send
(dGame) instead of writing to Game::chatServer by hand. eChatChannel,
eChatMessageResponseCode and eAddIgnoreResponse moved to dCommon/dEnums so the structs
can use them.

Verified: tests/dGameTests/dNetTests/Legacy/ChatPacketsLegacy.h is a verbatim copy of
the old senders and readers; ChatPacketsTests (25 tests) sends a grid of inputs through
both and requires identical bits, bytes and destination, checks the old readers read
what the structs write, round trips every struct, checks truncated packets are refused,
and has hand written golden packets for general chat, canned text, GM mute and a routed
team game message. Breaking one field width (UpdateFriendNotify) and the TeamAddPlayer
zone flag made the tests fail. No wire bytes changed.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

docs/PacketArchitecture.md

@@ -170,6 +170,16 @@ Every non-game-message packet is an `LUBitStream` subclass. The base owns the fu
   (`dChatServer`, `dMasterServer`, `dWorldServer`, `dAuthServer`) and are attached to the struct by overriding
   `Handle` in that server's translation unit.
 - Fixed-width strings use `LUString`/`LUWString` with the width spelled out (`LUWString password(41)`).
+- `PacketDispatcher<MessageType::X>` (`dNet/PacketDispatcher.h`) is the dispatch map for servers where the same
+  struct is handled differently depending on who receives it (chat, master, the dashboard): each entry names the
+  struct and a handler function `(const Msg&, const SystemAddress&)`. `Dispatch(packet, service)` reads the header,
+  reads the struct and drops (and logs) packets that fail to `Deserialize`.
+- Structs go in the file of the `ServiceType` in their header (`ChatPackets` for CHAT, `ClientPackets` for CLIENT,
+  `MasterPackets` for MASTER, ...), whoever sends them. What chat sends a client in the CLIENT service (friends,
+  ignore list and team responses, and the team game messages it writes as `ClientPackets::TeamGameMsg`, since chat
+  doesn't link `dGame`) is in `ClientPackets`; chat-service packets the client receives are in `ChatPackets::Client`.
+- Chat -> client packets are wrapped in `ChatPackets::WorldRoutePacket` (`dNet/WorldRoutePacket.h`: target object ID
+  + the inner packet of any service); the world passes the inner bytes on unchanged.
 
 ```cpp
 // dNet/ChatPackets.h