ShareLinks plugin: guest share links for Jellyfin

Includes fix for redemption failing with DbUpdateConcurrencyException:
change the guest password before applying the user policy, since
UpdatePolicyAsync bumps the user's EF concurrency token and a stale
instance then breaks ChangePassword.

Jellyfin.Plugin.ShareLinks/Services/NoOpShareLinkCleanupService.cs

@@ -0,0 +1,17 @@
+using System.Threading;
+using System.Threading.Tasks;
+
+namespace Jellyfin.Plugin.ShareLinks.Services;
+
+/// <summary>
+/// Temporary cleanup implementation used until the real cleanup pipeline lands.
+/// </summary>
+public sealed class NoOpShareLinkCleanupService : IShareLinkCleanupService
+{
+    /// <inheritdoc />
+    public Task CleanupAsync(CancellationToken cancellationToken)
+    {
+        _ = cancellationToken;
+        return Task.CompletedTask;
+    }
+}