feat(backend): add JWT authentication, RBAC and consent/audit services

Add signup/signin with backend-issued JWT (Argon2 passwords in SurrealDB), role-based authorization policies, per-user data access levels, consent register and read audit log. Protect user endpoints and record sensitive reads.

backend/Application/Abstractions/IUserService.cs

@@ -0,0 +1,15 @@
+using TarninaHub.Application.Dtos;
+using TarninaHub.Application.Models;
+
+namespace TarninaHub.Application.Abstractions;
+
+public interface IUserService
+{
+    Task<UserAccount?> FindByPhoneAsync(string phone, CancellationToken cancellationToken);
+
+    Task<UserAccount?> GetByIdAsync(string userId, CancellationToken cancellationToken);
+
+    Task<UserAccount?> CreateAsync(RegisterRequest request, string role, CancellationToken cancellationToken);
+
+    Task<bool> VerifyCredentialsAsync(string phone, string password, CancellationToken cancellationToken);
+}