feat: enforce tenant isolation and shared question bank

Tiku.Application/Tenancy/TenantDirectoryModels.cs

@@ -0,0 +1,22 @@
+using Tiku.Domain.Tenancy;
+
+namespace Tiku.Application.Tenancy;
+
+public sealed record TenantDirectoryEntry(
+    Guid TenantId,
+    string TenantCode,
+    string Name,
+    TenantStatus Status,
+    TenantMode Mode,
+    string? Host);
+
+public interface ITenantDirectory
+{
+    Task<TenantDirectoryEntry?> FindByHostAsync(
+        string host,
+        CancellationToken cancellationToken = default);
+
+    Task<TenantDirectoryEntry?> FindByCodeAsync(
+        string tenantCode,
+        CancellationToken cancellationToken = default);
+}