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/Lifecycle/StartupCleanupHostedService.cs

@@ -0,0 +1,42 @@
+using System;
+using System.Threading;
+using System.Threading.Tasks;
+using Jellyfin.Plugin.ShareLinks.Services;
+using Microsoft.Extensions.Hosting;
+using Microsoft.Extensions.Logging;
+
+namespace Jellyfin.Plugin.ShareLinks.Lifecycle;
+
+/// <summary>
+/// Runs one cleanup pass at startup so stale records do not linger forever.
+/// </summary>
+public sealed class StartupCleanupHostedService : BackgroundService
+{
+    private readonly IShareLinkCleanupService _cleanupService;
+    private readonly ILogger<StartupCleanupHostedService> _logger;
+
+    /// <summary>Initializes a new instance of the <see cref="StartupCleanupHostedService"/> class.</summary>
+    public StartupCleanupHostedService(
+        IShareLinkCleanupService cleanupService,
+        ILogger<StartupCleanupHostedService> logger)
+    {
+        _cleanupService = cleanupService;
+        _logger = logger;
+    }
+
+    /// <inheritdoc />
+    protected override async Task ExecuteAsync(CancellationToken stoppingToken)
+    {
+        try
+        {
+            await _cleanupService.CleanupAsync(stoppingToken).ConfigureAwait(false);
+        }
+        catch (OperationCanceledException) when (stoppingToken.IsCancellationRequested)
+        {
+        }
+        catch (Exception ex)
+        {
+            _logger.LogWarning(ex, "ShareLinks: startup cleanup failed.");
+        }
+    }
+}