first commit

Interfaces/Services/IPermissionService.cs

@@ -0,0 +1,13 @@
+using Microsoft.AspNetCore.Http;
+
+namespace Fitness_core_BE.Interfaces.Services
+{
+    public record PermissionContext(bool IsOwner, Guid? ClientId, Guid? StaffId, IReadOnlySet<string> AllowedNavKeys);
+
+    public interface IPermissionService
+    {
+        // Single shared source of truth for "what can this caller see/do" — used by both
+        // RequiresPermissionAttribute and NavController so they can never drift apart.
+        Task<PermissionContext> GetPermissionContextAsync(HttpContext httpContext);
+    }
+}