Sync from GitHub main: v0.1.1, v0.1.2, wiki sync

Squashes the work that landed on GitHub via PRs #2 (v0.1.1), #3
(v0.1.2), and #4 (wiki sync) into a single commit on Gitea so both
remotes converge. Content is identical to github/main; commit history
is split for branching reasons (Gitea was merged via PR #1 long ago,
GitHub used squash merges from then on, so the SHAs diverged).

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/WebhookServer.Core/Ipc/AdminProtocol.cs

@@ -26,6 +26,7 @@ public static class AdminOps
     public const string ListBackups = "list-backups";
     public const string RestoreBackup = "restore-backup";
     public const string ImportConfig = "import-config";
+    public const string CreateCheckpoint = "create-checkpoint";
 }
 
 public sealed class BackupEntry
@@ -33,6 +34,7 @@ public sealed class BackupEntry
     public string FileName { get; set; } = "";
     public DateTimeOffset SavedAt { get; set; }
     public long SizeBytes { get; set; }
+    public string? Description { get; set; }
 }
 
 public sealed class RestoreBackupArgs
@@ -40,6 +42,11 @@ public sealed class RestoreBackupArgs
     public string FileName { get; set; } = "";
 }
 
+public sealed class CreateCheckpointArgs
+{
+    public string? Description { get; set; }
+}
+
 public sealed class AdminRequest
 {
     [JsonPropertyName("op")] public string Op { get; set; } = "";