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/IAuditLogService.cs

@@ -0,0 +1,11 @@
+namespace TarninaHub.Application.Abstractions;
+
+public interface IAuditLogService
+{
+    Task RecordAsync(
+        string? actorId,
+        string action,
+        string target,
+        IReadOnlyDictionary<string, object?> context,
+        CancellationToken cancellationToken);
+}