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/Dtos/ConsentDtos.cs

@@ -0,0 +1,11 @@
+namespace TarninaHub.Application.Dtos;
+
+public sealed record GrantConsentRequest(string Scope, DateTimeOffset? ExpiresAt);
+
+public sealed record ConsentResponse(
+    string Id,
+    string UserId,
+    string Scope,
+    DateTimeOffset GrantedAt,
+    DateTimeOffset? ExpiresAt,
+    DateTimeOffset? RevokedAt);