feat(command-zone): add server-side support with tests

Implement server-side protocol and game logic for networked command
zone play.

Protocol changes:
- room_commands.proto: command zone messages and responses

Server components:
- ServerCounter: counter synchronization for commander tax
- ServerGame: command zone game state management
- ServerPlayer: player-level command zone handling
- Server/ServerProtocolHandler: command zone message routing
- Servatrice: command zone support in the main server

Design decisions:
- setCount() returns bool for event suppression (avoid duplicate events)
- Zone state synchronized across all connected clients
- Commander tax persists across zone transitions

Test coverage verifies setCount() return value behavior for proper
event suppression in networked scenarios.

libcockatrice_protocol/libcockatrice/protocol/pb/room_commands.proto

@@ -69,6 +69,15 @@ message Command_CreateGame {
 
     // share decklists with all players when selected
     optional bool share_decklists_on_load = 14;
+
+    // enable the command zone for Commander format
+    optional bool enable_command_zone = 15;
+
+    // enable companion zone for Ikoria mechanic
+    optional bool enable_companion_zone = 16;
+
+    // enable background zone for Baldur's Gate mechanic
+    optional bool enable_background_zone = 17;
 }
 
 message Command_JoinGame {