Update wire protocol to version 7 and enhance presence management features

- Bumped the wire protocol version to 7, reflecting significant changes in the communication structure.
- Introduced a new presence message type for real-time occupancy updates, including node activity and individual presence states.
- Updated the API to include a directory endpoint for fetching short id→name mappings, improving client-side name resolution.
- Revised the map snapshot structure to be static, with people and current lessons now handled through the presence stream.
- Enhanced client-side handling of presence updates, including UI adjustments to display live occupancy and activity.
- Updated documentation to reflect the new protocol features and changes in presence management.
- Added tests to validate the new presence functionalities and ensure robust handling of real-time data.

src/HSchool.Server/Game/GameCommand.cs

@@ -7,7 +7,7 @@ namespace HSchool.Server.Game;
 
 /// <summary>
 /// Work item handed from a request or connection thread to the supervisor. Create, delete and
-/// name suggestions stay here; open/close/running/speed are forwarded to the school's worker.
+/// name suggestions stay here; open/close/running/speed/skip are forwarded to the school's worker.
 /// </summary>
 internal abstract record GameCommand
 {
@@ -36,6 +36,8 @@ internal abstract record GameCommand
 
     internal sealed record SetSpeed(uint PlayerId, byte SpeedIndex) : GameCommand;
 
+    internal sealed record SkipEmpty(uint PlayerId) : GameCommand;
+
     /// <summary>Stops every worker, re-reads the save directory, starts workers from those files.</summary>
     internal sealed record ReloadSaves(TaskCompletionSource Result) : GameCommand;