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/Models/UserAccount.cs

@@ -0,0 +1,8 @@
+namespace TarninaHub.Application.Models;
+
+public sealed record UserAccount(
+    string Id,
+    string Phone,
+    string? Email,
+    string Role,
+    string? OrganizationId);