Update wire protocol to version 6 and enhance timetable functionality

- Bumped the wire protocol version to 6, reflecting changes in the communication structure.
- Expanded the timetable API with new endpoints for fetching and managing lesson schedules, including `GET /api/schools/{id}/timetable` and `POST /api/schools/{id}/timetable/pin`.
- Updated the protocol documentation to include detailed descriptions of the new timetable features and message structures.
- Enhanced the client-side implementation to support the new timetable functionalities, including lesson pinning and unpinning.
- Revised server-side logic to handle timetable operations and ensure proper integration with existing school management features.
- Added tests to validate the new timetable functionalities and ensure robustness in handling lesson data.

src/HSchool.Protocol/ProtocolCodec.cs

@@ -129,6 +129,18 @@ public static class ProtocolCodec
             {
                 size += StringSize(position);
             }
+
+            size += sizeof(byte);
+            if (HasActivity(node))
+            {
+                size += StringSize(node.ActivitySubject) + StringSize(node.ActivityClass);
+            }
+
+            size += sizeof(byte);
+            foreach (var person in node.Present)
+            {
+                size += StringSize(person);
+            }
         }
 
         return size;
@@ -148,9 +160,9 @@ public static class ProtocolCodec
 
         foreach (var node in message.Nodes)
         {
-            if (node.Items.Count > byte.MaxValue || node.Positions.Count > byte.MaxValue)
+            if (node.Items.Count > byte.MaxValue || node.Positions.Count > byte.MaxValue || node.Present.Count > byte.MaxValue)
             {
-                throw new ProtocolException($"Map node '{node.Id}' has too many items or positions for a u8 count.");
+                throw new ProtocolException($"Map node '{node.Id}' has too many items, positions or people for a u8 count.");
             }
 
             writer.WriteByte(node.Kind);
@@ -170,6 +182,23 @@ public static class ProtocolCodec
             {
                 writer.WriteString(position);
             }
+
+            if (HasActivity(node))
+            {
+                writer.WriteByte(1);
+                writer.WriteString(node.ActivitySubject);
+                writer.WriteString(node.ActivityClass);
+            }
+            else
+            {
+                writer.WriteByte(0);
+            }
+
+            writer.WriteByte((byte)node.Present.Count);
+            foreach (var person in node.Present)
+            {
+                writer.WriteString(person);
+            }
         }
 
         return writer.Position;
@@ -283,12 +312,41 @@ public static class ProtocolCodec
                 positions[position] = reader.ReadString();
             }
 
-            nodes[i] = new MapSnapshotNode(kind, id, parentId, name, pupilSlots, items, positions);
+            var hasActivity = reader.ReadByte() != 0;
+            var activitySubject = "";
+            var activityClass = "";
+            if (hasActivity)
+            {
+                activitySubject = reader.ReadString();
+                activityClass = reader.ReadString();
+            }
+
+            var characterCount = reader.ReadByte();
+            var characters = new string[characterCount];
+            for (var person = 0; person < characterCount; person++)
+            {
+                characters[person] = reader.ReadString();
+            }
+
+            nodes[i] = new MapSnapshotNode(
+                kind,
+                id,
+                parentId,
+                name,
+                pupilSlots,
+                items,
+                positions,
+                activitySubject,
+                activityClass,
+                characters);
         }
 
         return new ServerMapSnapshotMessage(schoolId, nodes);
     }
 
+    private static bool HasActivity(MapSnapshotNode node) =>
+        node.ActivitySubject.Length > 0 || node.ActivityClass.Length > 0;
+
     /// <summary>Matches <see cref="PacketWriter.WriteString"/>: a <c>u16</c> length plus UTF-8.</summary>
     private static int StringSize(string value) => sizeof(ushort) + Encoding.UTF8.GetByteCount(value);