feat(core): add models for institution

src/FiscalOS.Core/Identity/User.cs

@@ -2,15 +2,17 @@ namespace FiscalOS.Core.Identity;
 
 public sealed class User : Entity
 {
-  private readonly List<RefreshToken> _refreshTokens = [];
-
   public string Username { get; init; } = string.Empty;
   public string HashedPassword { get; init; } = string.Empty;
   public string EncryptionKeyId { get; init; } = string.Empty;
   public string EncryptedDataKey { get; init; } = string.Empty;
 
+  private readonly List<RefreshToken> _refreshTokens = [];
   public IEnumerable<RefreshToken> RefreshTokens => _refreshTokens;
 
+  private readonly List<Institution> _institutions = [];
+  public IEnumerable<Institution> Institutions => _institutions;
+
   private User()
   {
   }
@@ -41,4 +43,11 @@ public sealed class User : Entity
 
     _refreshTokens.Add(refreshToken);
   }
+
+  public void AddInstitution(Institution institution)
+  {
+    ArgumentNullException.ThrowIfNull(institution);
+
+    _institutions.Add(institution);
+  }
 }