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.Protocol/Messages.cs

@@ -31,12 +31,16 @@ public readonly record struct ServerPongMessage(long ClientTimeMs, uint ServerTi
 /// State of the open school's calendar, sent every tick.
 /// <paramref name="GameTimeUnixMs"/> is the in-game date as milliseconds since the Unix epoch,
 /// interpreted as UTC — the game calendar has no time zone.
+/// <paramref name="SkipAllowed"/> is the server's verdict; the client must not recompute it.
+/// <paramref name="SkipTargetUnixMs"/> is 0 when skip is refused.
 /// </summary>
 public readonly record struct ServerClockMessage(
     int SchoolId,
     long GameTimeUnixMs,
     bool Running,
-    byte SpeedIndex);
+    byte SpeedIndex,
+    bool SkipAllowed = false,
+    long SkipTargetUnixMs = 0);
 
 /// <summary>The open school no longer exists (deleted from another tab); the client returns to the menu.</summary>
 public readonly record struct ServerSchoolGoneMessage(int SchoolId);
@@ -45,9 +49,7 @@ public readonly record struct ServerSchoolGoneMessage(int SchoolId);
 /// Tree node in a map snapshot. Kind is <c>0</c> territory, <c>1</c> building, <c>2</c> floor, <c>3</c> room.
 /// <paramref name="ParentId"/> is empty for the yard.
 /// <paramref name="PupilSlots"/> is how many pupils can take a lesson here — summed from things
-/// on the server, not by the client.
-/// <paramref name="ActivitySubject"/> and <paramref name="ActivityClass"/> are empty when the
-/// room is free. <paramref name="Characters"/> are the people the timetable puts there right now.
+/// on the server, not by the client. Live occupancy lives on <see cref="ServerPresenceMessage"/>.
 /// </summary>
 public sealed record MapSnapshotNode(
     byte Kind,
@@ -56,19 +58,42 @@ public sealed record MapSnapshotNode(
     string Name,
     ushort PupilSlots,
     IReadOnlyList<MapSnapshotItem> Items,
-    IReadOnlyList<string> Positions,
-    string ActivitySubject = "",
-    string ActivityClass = "",
-    IReadOnlyList<string>? Characters = null)
-{
-    public IReadOnlyList<string> Present => Characters ?? [];
-}
+    IReadOnlyList<string> Positions);
 
 /// <summary>One stacked thing in a room. <paramref name="Count"/> is 1–255.</summary>
 public sealed record MapSnapshotItem(string Name, byte Count);
 
 /// <summary>
-/// One school's map, labelled in the Hello locale. Sent when that school is opened and again
-/// when the current lesson slot changes. Occupancy is computed from the timetable and the clock.
+/// One school's map, labelled in the Hello locale. Sent once when that school is opened.
+/// Structure only — people and the current lesson ride the presence stream.
 /// </summary>
 public sealed record ServerMapSnapshotMessage(int SchoolId, IReadOnlyList<MapSnapshotNode> Nodes);
+
+/// <summary>Jump empty nights, weekends and holidays. The server re-checks the conditions.</summary>
+public readonly record struct ClientSkipEmptyMessage;
+
+/// <summary>Where people are: 1 in a node, 2 walking through it. Off campus is omitted.</summary>
+public static class PresenceState
+{
+    public const byte Here = 1;
+    public const byte Walking = 2;
+}
+
+/// <summary>One occupied (or currently taught) map node in a presence frame.</summary>
+public sealed record PresenceNode(
+    string Id,
+    ushort Count,
+    string ActivitySubject = "",
+    string ActivityClass = "");
+
+/// <summary>One on-campus person. Names are resolved over HTTP, not on this frame.</summary>
+public sealed record PresencePerson(string Id, string NodeId, byte State);
+
+/// <summary>
+/// Live occupancy of an open school, about twice a second. Counts and people cover the whole
+/// map; the client filters to the selected tree node.
+/// </summary>
+public sealed record ServerPresenceMessage(
+    int SchoolId,
+    IReadOnlyList<PresenceNode> Nodes,
+    IReadOnlyList<PresencePerson> People);