feat(chat): keep activity lobbies of every world and start their instances through master

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

dChatServer/ChatMatchmaking.h

@@ -0,0 +1,34 @@
+#ifndef CHATMATCHMAKING_H
+#define CHATMATCHMAKING_H
+
+#include "dCommonVars.h"
+#include "Matchmaking.h"
+
+struct SystemAddress;
+
+namespace ChatPackets {
+	struct MatchRequest;
+}
+
+/**
+ * The chat server's activity matchmaking (docs/Matchmaking.md): lobbies across every world. Worlds send the players'
+ * lobby joins, readies and leaves; lobby updates go to the clients through their worlds; when a countdown runs out
+ * master starts one instance of the activity's zone and each player's world is told to send them there.
+ * Runs on the chat server's main thread only.
+ */
+namespace ChatMatchmaking {
+	void HandleMatchRequest(const ChatPackets::MatchRequest& request, const SystemAddress& sysAddr);
+
+	// The player left their world (logged out, or loaded into another one): they leave their lobby
+	void PlayerLeftWorld(LWOOBJID playerID);
+
+	// Once a frame: the lobby countdowns
+	void Update(float deltaTime);
+
+	// Starts the instance of a formed match and tells the players' worlds (also used by tests)
+	void StartMatch(const Matchmaking::Match& match);
+
+	Matchmaking::Lobbies& GetLobbies();
+}
+
+#endif // CHATMATCHMAKING_H