feat: Recently Added Guard plugin for Jellyfin 12.2

Keeps Radarr/Sonarr quality upgrades out of "Recently Added" by keeping
a ledger of the first date added per logical medium (movie or episode,
identified by provider ids and the series) and restoring it on upgrades.

- core logic without Jellyfin types (Reconciler, MediaKeys, GuardProcessor)
- thread-safe ledger with atomic, debounced persistence
- event processing via channel and background worker, seed on first start
- scheduled task "Ledger synchronisieren", status API, configuration page
- xUnit tests and a Jellyfin 12.2 integration test
- Gitea workflows: build/test, release with jprm and manifest branch

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

Jellyfin.Plugin.RecentlyAddedGuard/Api/GuardController.cs

@@ -0,0 +1,76 @@
+using System.Net.Mime;
+using Jellyfin.Plugin.RecentlyAddedGuard.Core;
+using Jellyfin.Plugin.RecentlyAddedGuard.Ledger;
+using Jellyfin.Plugin.RecentlyAddedGuard.Tasks;
+using MediaBrowser.Common.Api;
+using MediaBrowser.Model.Tasks;
+using Microsoft.AspNetCore.Authorization;
+using Microsoft.AspNetCore.Http;
+using Microsoft.AspNetCore.Mvc;
+
+namespace Jellyfin.Plugin.RecentlyAddedGuard.Api;
+
+/// <summary>
+/// Status and actions for the configuration page. Jellyfin adds plugin assemblies as MVC application parts,
+/// so this controller is discovered automatically.
+/// </summary>
+[ApiController]
+[Route("RecentlyAddedGuard")]
+[Authorize(Policy = Policies.RequiresElevation)]
+[Produces(MediaTypeNames.Application.Json)]
+public class GuardController : ControllerBase
+{
+    private readonly LedgerStore _store;
+    private readonly CorrectionLog _corrections;
+    private readonly ITaskManager _taskManager;
+
+    /// <summary>
+    /// Initializes a new instance of the <see cref="GuardController"/> class.
+    /// </summary>
+    /// <param name="store">The ledger.</param>
+    /// <param name="corrections">The correction log.</param>
+    /// <param name="taskManager">The task manager.</param>
+    public GuardController(LedgerStore store, CorrectionLog corrections, ITaskManager taskManager)
+    {
+        _store = store;
+        _corrections = corrections;
+        _taskManager = taskManager;
+    }
+
+    /// <summary>
+    /// Gets ledger statistics and the most recent corrections.
+    /// </summary>
+    /// <response code="200">The status.</response>
+    /// <returns>The status.</returns>
+    [HttpGet("Status")]
+    [ProducesResponseType(StatusCodes.Status200OK)]
+    public ActionResult<GuardStatus> GetStatus()
+    {
+        var statistics = _store.GetStatistics();
+        return new GuardStatus
+        {
+            LedgerEntries = statistics.Entries,
+            LiveEntries = statistics.LiveEntries,
+            RemovedEntries = statistics.RemovedEntries,
+            CorrectionsSinceStart = _corrections.CorrectionsSinceStart,
+            DryRunDetectionsSinceStart = _corrections.DryRunDetectionsSinceStart,
+            SeedCompleted = _store.SeedCompleted,
+            LastSyncUtc = _store.LastSyncUtc,
+            DryRun = Plugin.CurrentConfiguration.DryRun,
+            RecentCorrections = _corrections.GetRecent()
+        };
+    }
+
+    /// <summary>
+    /// Queues the scheduled task "Ledger synchronisieren".
+    /// </summary>
+    /// <response code="204">The task was queued (or is already running).</response>
+    /// <returns>No content.</returns>
+    [HttpPost("Sync")]
+    [ProducesResponseType(StatusCodes.Status204NoContent)]
+    public ActionResult StartSync()
+    {
+        _taskManager.QueueIfNotRunning<SyncLedgerTask>();
+        return NoContent();
+    }
+}