feat: add seating plans for learning groups

LehrerApp.Core/Models/SeatingPlan.cs

@@ -0,0 +1,25 @@
+namespace LehrerApp.Core.Models;
+
+/// <summary>
+/// Ein Sitzplan einer Lerngruppe. Eine Gruppe kann mehrere Pläne besitzen,
+/// beispielsweise für unterschiedliche Unterrichtsräume.
+/// </summary>
+public class SeatingPlan
+{
+    public Guid Id { get; set; } = Guid.NewGuid();
+    public Guid GroupId { get; set; }
+    public string Name { get; set; } = "";
+    public string Room { get; set; } = "";
+    public int Rows { get; set; } = 4;
+    public int Columns { get; set; } = 4;
+    public List<SeatAssignment> Assignments { get; set; } = [];
+    public DateTime CreatedAt { get; set; } = DateTime.UtcNow;
+    public DateTime UpdatedAt { get; set; } = DateTime.UtcNow;
+}
+
+public class SeatAssignment
+{
+    public int Row { get; set; }
+    public int Column { get; set; }
+    public Guid StudentId { get; set; }
+}