feat: add core persistence model

Tiku.Domain/Tenancy/TenantMembership.cs

@@ -0,0 +1,32 @@
+using System.Text.Json;
+using Tiku.Domain.Common;
+
+namespace Tiku.Domain.Tenancy;
+
+public sealed class TenantMembership : AuditableTenantEntity
+{
+    public Guid UserId { get; set; }
+    public TenantRole Role { get; set; } = TenantRole.Student;
+    public MembershipStatus Status { get; set; } = MembershipStatus.Active;
+    public JsonElement Permissions { get; set; } = JsonDefaults.Object();
+    public string? LegacyRole { get; set; }
+}
+
+public enum TenantRole
+{
+    PlatformAdmin,
+    TenantOwner,
+    TenantAdmin,
+    TenantOperator,
+    Teacher,
+    Sales,
+    Agent,
+    Student
+}
+
+public enum MembershipStatus
+{
+    Active,
+    Invited,
+    Disabled
+}