feat: enforce tenant isolation and shared question bank

Tiku.Application/Catalog/TaxonomyModels.cs

@@ -0,0 +1,36 @@
+using System.Text.Json;
+using Tiku.Domain.Catalog;
+using Tiku.Domain.Content;
+
+namespace Tiku.Application.Catalog;
+
+public sealed record TaxonomyNodeItem(
+    Guid Id,
+    QuestionSource Source,
+    Guid? ParentId,
+    QuestionSource? ParentSource,
+    TaxonomyNodeType NodeType,
+    string Code,
+    string Name,
+    string? Path,
+    int Depth,
+    int SortOrder,
+    JsonElement Metadata);
+
+public sealed record CreateTaxonomyNodeCommand(
+    Guid? ParentId,
+    QuestionSource? ParentSource,
+    TaxonomyNodeType NodeType,
+    string Code,
+    string Name,
+    int SortOrder,
+    JsonElement Metadata);
+
+public interface ITaxonomyService
+{
+    Task<IReadOnlyCollection<TaxonomyNodeItem>> ListAsync(Guid tenantId, CancellationToken cancellationToken = default);
+    Task<TaxonomyNodeItem> CreateAsync(
+        Guid tenantId,
+        CreateTaxonomyNodeCommand command,
+        CancellationToken cancellationToken = default);
+}