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/GuardStatus.cs

@@ -0,0 +1,56 @@
+using System;
+using System.Collections.Generic;
+using Jellyfin.Plugin.RecentlyAddedGuard.Core;
+
+namespace Jellyfin.Plugin.RecentlyAddedGuard.Api;
+
+/// <summary>
+/// Status shown on the configuration page.
+/// </summary>
+public sealed class GuardStatus
+{
+    /// <summary>
+    /// Gets the number of ledger entries.
+    /// </summary>
+    public int LedgerEntries { get; init; }
+
+    /// <summary>
+    /// Gets the number of entries with at least one live item.
+    /// </summary>
+    public int LiveEntries { get; init; }
+
+    /// <summary>
+    /// Gets the number of entries whose items are gone (within the grace period).
+    /// </summary>
+    public int RemovedEntries { get; init; }
+
+    /// <summary>
+    /// Gets the number of corrections since the server started.
+    /// </summary>
+    public long CorrectionsSinceStart { get; init; }
+
+    /// <summary>
+    /// Gets the number of upgrades detected in dry-run mode since the server started.
+    /// </summary>
+    public long DryRunDetectionsSinceStart { get; init; }
+
+    /// <summary>
+    /// Gets a value indicating whether the initial seed has completed.
+    /// </summary>
+    public bool SeedCompleted { get; init; }
+
+    /// <summary>
+    /// Gets the time of the last seed or synchronization (UTC).
+    /// </summary>
+    public DateTime? LastSyncUtc { get; init; }
+
+    /// <summary>
+    /// Gets a value indicating whether dry-run mode is active.
+    /// </summary>
+    public bool DryRun { get; init; }
+
+    /// <summary>
+    /// Gets the most recent corrections, newest first.
+    /// </summary>
+    public IReadOnlyList<CorrectionRecord> RecentCorrections { get; init; } = [];
+}