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/Configuration/PluginConfiguration.cs

@@ -0,0 +1,41 @@
+using Jellyfin.Plugin.RecentlyAddedGuard.Core;
+using MediaBrowser.Model.Plugins;
+
+namespace Jellyfin.Plugin.RecentlyAddedGuard.Configuration;
+
+/// <summary>
+/// The plugin configuration.
+/// </summary>
+public class PluginConfiguration : BasePluginConfiguration
+{
+    /// <summary>
+    /// Gets or sets the number of days within which a returning medium counts as an upgrade.
+    /// </summary>
+    public int GraceDays { get; set; } = 14;
+
+    /// <summary>
+    /// Gets or sets a value indicating whether movies are protected.
+    /// </summary>
+    public bool EnableMovies { get; set; } = true;
+
+    /// <summary>
+    /// Gets or sets a value indicating whether episodes are protected.
+    /// </summary>
+    public bool EnableEpisodes { get; set; } = true;
+
+    /// <summary>
+    /// Gets or sets a value indicating whether upgrades are only logged, not corrected.
+    /// </summary>
+    public bool DryRun { get; set; }
+
+    /// <summary>
+    /// Gets or sets the tolerance in seconds for comparing dates.
+    /// </summary>
+    public int ToleranceSeconds { get; set; } = 60;
+
+    /// <summary>
+    /// Maps the configuration to the options of the core logic.
+    /// </summary>
+    /// <returns>The options.</returns>
+    public GuardOptions ToGuardOptions() => new(GraceDays, ToleranceSeconds, DryRun);
+}